GENERAL   SUGGESTIONS   TO   THE   STUDENT 


1.  Solids  —  like  match  sticks,  bits  of  glass  or  metal  —  should  never 
be  thrown  into  the  sinks.     They  clog  the  plumbing  and  cause  great 
annoyance  and  damage.      Put  them  in  the  waste  jars   provided  for" 
the  purpose. 

2.  Paper  is  out  of  place  in  the  sinks.      It  is  dangerous  to  put  it 
in  the  waste  jars,  where  it  often  takes  fire.     The  proper  place  for  it 
is  the  waste-paper  basket. 

3.  The  student  will  find  that  he  has  a  strong  tendency  to  take 
too   much   of   the   various    substances   required   in   his    work.       This 
tendency  must  be  overcome  before   any  real    progress  can   be  made. 
The  quantity  needed  is  stated  in  each  study.     To  take  more  means 
wast^  of  material  and  of  time. 

4.  Never  pour  water  into  concentrated  sulphuric  acid.     In  diluting 
sulphuric  acid,  the  acid  should  be  added  to  the  water  in  a  thin  stream, 
with  Constant  stirring. 

5.  When  it  is  necessary  to  mix  ammonia  with  an  acid,  both  should 
be    d' luted   before    mixing.     Explosive  interaction  occurs  when  con- 
centrated ammonia  is  mixed  with  concentrated  acids. 

6.  Before  using  a  vessel,  make  sure  that  it  is  dean.     Experiments 
in  dirty  vessels  are  not  worth  making,  for  the  results  are  only  mis- 
leading. 

7.  |  Learn  to  regulate  the  height  of  your  burner  flame.     For  heating 
test  tibes  and  beakers,  a  small  flame  is  better  than  a  large  one. 

8.  (Take  at  least  five  minutes  at  the  end  of  each  laboratory  period 
to  clean  up  your  glassware  and  put  your  working  place  in  order. 

THE  NOTEBOOK 

9.  Neat,  full,  and  accurate  notes  are  necessary,  especially  to  those 
of  you  who  expect  to  obtain  credit  for  your  chemical  work  in  college, 
university,  or  before  any  examining  board.     Do  not  copy  the  directions 
from  ihe,  manual.     State,  in  your  own  way,  the  object  of  each  experi- 
ment, the  method  and  apparatus,  the  results,  and  your  conclusions. 
Frequently,  a  simple  line  drawing,  similar  to  those  in  the  textbook, 
will  make  your  description  easier  to  understand.     The  notebook  should 
be  provided  with  an  index. 


GIFT  OF 


TWENTIETH   CENTURY  TEXT-BOOKS 


LABORATOKY  STUDIES 
IN  CHEMISTRY 


BY 
ROBERT   H.    BRADBURY,  A.M.,  PH.D. 

HEAD    OF    THE    DEPARTMENT    OF    SCIENCE    IN    THE 
SOUTHERN    HIGH    SCHOOL,    PHILADELPHIA 


D.    APPLETON    AND    COMPANY 

NEW    YORK  CHICAGO 


TWENTIETH  CENTURY  TEXT-BOOKS 


COPYRIGHT,  1912, 
BY  D.  APPLETON  AND  COMPANY. 


PREFACE 

Briefly  stated,  the  main  features  of  this  laboratory  manual 
are  as  follows  :  — 

1.  It  covers  thoroughly  the  various  syllabi  which  teachers 
preparing  students  for  college  have  to  consider. 

2.  Each  exercise,  including  the  writing  of  the  notes,  can  be 
finished  within  ninety  minutes. 

3.  The  apparatus  required  is  simple  and  inexpensive,  and 
due  regard  has  been  given  to   the   prices   of  the   chemicals. 
Expensive  substances  are  employed  at  times,  but  only  in  very 
small  quantities. 

4.  The  fact  has  not  been  overlooked  that  the  teacher  of 
science  usually  carries   as    many  hours  on   the  roster  as  the 
teacher  who  has  no  apparatus  or  materials  to  arrange.     I  have 
tried  to  simplify  the  manual  labor   required  of  the  teacher, 
without  reducing  the  efficiency  of  the  work. 

5.  The  experienced  teacher  will  at  once  perceive  that  the 
practical  details  of  the   experiments   have   been  worked  out 
with  unusual  care.     It  has,  in  fact,  taken  me  many  years  to 
get  these  laboratory  studies  into  the  shape  in  which  they  are 
here  presented,  and  I  have  refrained   from  publishing  them 
until  I  had  made  sure  that  they  wefe  as  perfect  as  the  pains- 
taking labor  of  my  students  and  myself  could  make  them.     I 
shall  be  very  grateful  indeed  for  any  suggestions  as  to  further 
improvements  from  other  teachers. 

It  is,  of  course,  as  impossible  as  it  is  undesirable  to  frame  a 
set  of  directions  which  shall  be  a  substitute  for  the  teacher. 
What  I  have  tried  to  do  is  merely  to  save  the  appalling  waste 
of  energy  involved  in  the  constant  repetition  of  details  such 

iii 

264202 


iv  PREFACE 

as  quantity  needed,  vessel  to  use,  height  of  flame,  dilution,  etc. 
To  supply  this  sort  of  information  is  precisely  the  function  of 
the  laboratory  manual. 

6.  It  is  not  at  all  difficult,  at  present,  to  put  together  a  set 
of  exercises  which  will  occupy   the   laboratory  .time   of  the 
beginner   for   a  year   in  a  pleasant  and   orderly  way.     It  is 
less  easy  to  make  sure  that  each  experiment  is  significant  and 
worth  while,  that  it  adds   something  to  the  logical  develop- 
ment of  the  student's  ideas  and  to  his   appreciation   of  the 
general  points  of  view  of  the  science.     I  confess  that  much 
that   is   offered  under  the  caption  of   laboratory  work  seems 
to  me  hardly  worth  the  time   it   takes.      The  student  who 
comes   to   the  laboratory   might  otherwise   be  doing  serious 
work  of  permanent  value   in   languages   or   in   mathematics. 
His  time  should  not   be  wasted  with  purely  spectacular  and 
pyrotechnic  experiments,  or  with  so-called  quantitative  studies, 

—  like  the  heating  of  magnesium  powder  —  in  which  even  the 
most  finished  experimental  technique  must  fail  to  secure  rea- 
sonably exact  results. 

One  of  the  chief  devices  I  have  employed  in  attempting  to 
give  greater  educational  value  to  the  work  is  classification. 
For  instance,  the  facts  which  relate  to  some  central  topic  such 
as  the  action  of  soluble  hydroxides  on  salt  solutions,  or  the 
effect  of  heat  upon  carbonates,  are  not  scattered  through  the 
book  in  a  wholly  aimless  way :  they  are  organized  into  a 
compact  laboratory  exercise  which  serves,  once  for  all,  to  make 
the  matter  clear.  Examples  of  this  general  principle  of  ar- 
rangement will  be  found  in  the  exercises  numbered  14,  22, 
31,  37,  58,  59,  and  others. 

7.  Probably  all  teachers  agree,  nowadays,  that  some  of  the 
work  should  be  quantitative.     The   quantitative   experiments 
in  this   book   have  been  worked   out  with   the  utmost   care. 
Since   I   have,  in  my  notebooks,  upwards  of   a  thousand  re- 
sults for  each  of  them,  I  may  fairly  say  that  they  are  quite 
within  the   capacity  of  high   school   students,  who,  in  fact, 


PREFACE  V 

work  them  out  with  enthusiastic  interest.  Naturally,  the 
effect  in  improving  the  manipulative  technique  of  the  students 
is  very  marked.  Far  more  important  is  the  reality  which  is 
given  to  their  conceptions  of  the  foundations  of  the  science. 
It  is  almost  impossible  to  teach  quantitative  ideas  without 
quantitative  experimentation  to  give  substance  to  the  teaching. 

A  balance  sensitive  to  a  milligram  can  now  be  bought  for 
about  ten  dollars.  Small  weights,  which  may  be  lost  from 
the  set,  can  be  easily  and  cheaply  replaced  by  cut  lengths  of 
No.  36  German  silver  wire,  B.  &  S.  gauge,  one  centimeter  of 
which  weighs  almost  exactly  one  milligram.  The  rest  of  the 
apparatus  required' is  of  the  simplest  description. 

8.  The  literature  of  the  elementary  laboratory  is  now  quite 
extensive,  and  I  have  tried  to  make  a  careful  survey  of  it. 
Among  the  books  which  have  been  most  helpful  are  Stoddard's 
Quantitative  Experiments  in  General  Chemistry,  Karl  Scheid's 
Praktischer  Unterriclit  in  CJiemie,  Ohmann's  Chemie,  and  the 
Laboratory  Manual  of  Alexander  Smith. 

The  quantity  of  material  required  in  the  experiments  is,  in 
all  cases,  stated  in  a  precise  numerical  way.  These  statements 
are  intended  simply  to  give  the  student  a  good  approximate 
idea  of  the  amount  he  should  take.  It  is  only  in  the  quantita- 
tive exercises  that  the  quantity  stated  should  be  accurately 
weighed  or  measured.  The  apparatus  and  materials  needed 
are  stated  at  the  beginning  of  each  exercise.  Supplies  always 
on  the  student's  table,  such  as  the  burner,  the  stand,  and  the 
ordinary  acids,  are  omitted. 

A  lead  disk  about  6x2  cm.,  pierced  radially  and  axially  is 
convenient  for  collecting  gases  over  water.  It  is  used  in  an 
agate  pan,  the  bottle  of  water  being  inverted  over  the  central 
perforation.  The  disk  also  has  been  omitted  from  the  lists  of 
necessary  supplies,  since  there  are  many  other  devices  which 
may  serve  the  purpose  equally  well. 

It  may  not  be  amiss  to  call  the  attention  of  teachers  to  the 
use  of  potassium  permanganate,  instead  of  manganese  dioxide, 


vi  PREFACE 

for  generating  chlorine,  and  of  formic  acid,  instead  of  oxalic 
acid,  in  the  preparation  of  carbon  monoxide.  In  both  cases, 
the  older  methods  have  been  obsolete  among  chemists  for 
some  years,  and  one  cannot  help  wondering  at  the  misplaced 
conservatism  which  causes  their  continued  republication  in  the 
newer  elementary  texts. 

It  is  not  improbable  that  chemists  who  are  not  engaged  in 
secondary  teaching  may  be  surprised  at  the  care  which  has 
been  taken  to  exclude  complex  and  expensive  apparatus.  Let 
me  add,  therefore,  that  the  secondary  school  teacher  handles 
sections  of  thirty  or  more  without  laboratory  assistance  and 
without  time  for  preparation,  that  he  must  finish  his  exercise 
in  a  definite  time,  which  is  usually  not  greater  than  ninety 
minutes,  and  that  his  students  have  had  no  opportunity  to 
acquire  manipulative  skill.  When  these  conditions  are  gen- 
erally understood,  a  certain  amount  of  energy,  which  is  now 
wasted  in  rather  futile  criticism  of  secondary  aims  and 
methods,  will  be  expended  in  some  more  useful  way.  In  fact, 
to  do  the  best  that  can  be  done  under  these  circumstances 
forms  a  difficult  problem,  which  is  quite  different  from  the 
problem  of  the  college  or  university  instructor.  To  offer,  in 
a  small  way,  some  help  toward  the  solution  of  the  problem  of 
elementary  teaching  is  the  object  of  the  present  book. 

Professor  Alfred  L.  Carey  of  the  Southern  High  School  has 
assisted  me  with  the  reading  of  the  proof.  The  illustrations 
are  from  original  drawings  made  by  my  wife. 

ROBERT   H.   BRADBURY. 


CONTENTS 


1.  Glass  Rod.     Tubing 1 

2.  Capacity  of  Laboratory  Vessels 3 

3.  Density  of  Liquids 4 

4.  Density  of  Sulphur,  Copper  Sulphate,  and  Marble         .        .  5 

5.  Sulphur (J 

6.  Galenite.     The  Use  of  the  Blowpipe 8 

7.  Pyrite 9 

8.  Chalcopyrite  {Copper  Pyrite) 10 

9.  Artificial  Sulphur-Compounds 11 

10.  Synthesis  of  Copper  Sulphide  (Cuprous)  (Quantitative")         .  13 

11.  The  Cyanide  Process  for  extracting  Gold  from  its  Ores         .  15 

12.  The  Effect  of  Heat  on  Wood  and  Soft  Coal  ....  16 

13.  Wood  Charcoal  and  Animal  Charcoal  (Boneblack)       .         .  16 

14.  Heating  Metals  in  the  Air 17 

15.  The  Combustion  of  Phosphorus  in  an  Enclosed  Volume  of 

Air 18 

16.  The  Percentage  of  Oxygen  in  Air 19 

17.  Chemical  Nitrogen 21 

18.  Oxygen  (Preliminary  Experiments)         .....  22 

19.  Oxygen  (Preparation) 23 

20.  Carbon  Dioxide  (Preliminary  Experiments)    ....  25 

21.  Preparation  of  Carbon  Dioxide 27 

22.  The  Action  of  Carbon  on  Oxides  of  Metals  ....  28 

23.  Arsenolite  (Arsenious  Oxide}  and  Arsenic      ....  29 

24.  Carbon  Monoxide 30 

25.  The  Atomic  Weight  of  Tin  (Quantitative)     ....  32 

26.  The  Distillation  of  Water 33 

27.  Crystallization 34 

28.  Preparation  of  Crystallized  Sodium  Carbonate      ...  35 

29.  Solution  (1) 35 

30.  Solution  (2) 37 

31.  Water  of  Crystallization 39 

vii 


viii  CONTENTS 

EXERCISE  PAGE 

32.  Water  of  Crystallization  (Quantitative)          .        .        .        .40 

33.  The  Action  of  Zinc  and  Iron  on  Water          .        .        .        .41 

34.  The  Interaction  of  Sodium  and  Water 43 

35.  The  Interaction  of  Calcium  and  Water 44 

36.  Hydrogen 45 

37.  Flame 47 

38.  Hydrogen  Sulphide 50 

39.  Ammonia         ..........  51 

40.  Neutralization  of  Ammonium  Hydroxide  by  Acids  (Ammo- 

nium Salts) 53 

41.  Methane 55 

42.  Carbohydrates 56 

43.  Acetic  Acid,  Wood  Alcohol,  Acetylene 57 

44.  Chlorine 59 

45.  The  Action  of  Sulphuric  Acid  on  Chlorides  ....  62 

46.  The  Action  of  Sulphuric  Acid  on  Salt 63 

47.  The  Action  of   Hydrochloric  Acid  on   Sodium   Hydrogen 

Sulphate 64 

48.  The  Action  of  Hydrochloric  Acid  upon  Metals      ...  64 

49.  The  Action  of  Hydrochloric  Acid  upon  Oxides     ...  66 

50.  Flame  Tests 67 

51.  Preparation  of  Sodium  Hydrogen  Carbonate  and  Sodium 

Carbonate  (Solvay  Process) 68 

52.  Hydrogen  Fluoride          .         .        .         .         .        .         .         .69 

53.  Bromine 71 

54.  Iodine 73 

55.  Silver  Compounds  of  the  Halogens  (The  Replacement  of  One 

Halogen  by  Another) 75 

56.  Neutralization  (1) 77 

57.  Neutralization  (2)  (Quantitative) 78 

58.  The  Action  of  Bases  on  Salts 80 

59.  The  Action  of  a  Metal  on  a  Solution  of  a  Salt  of  Another 

Metal 82 

60.  Ionized  and  Un-ionized  Solutions  ......  84 

61.  Hydrolysis 85 

62.  Separation  of  Lead,  Silver,  and  Mercury        ....  87 

63.  The  Bead  Tests 89 

64.  Dyeing 92 

65.  Nitric  Acid,  Aqua  Regia         . 94 


CONTENTS  ix 

EXERCISE  PAGE 

66.  Potassium  Nitrate 96 

67.  Preparation  of  Sodium  Nitrite 97 

68.  Nitric  Oxide 98 

69.  Nitrous  Oxide 99 

70.  Phosphate  Fertilizers 101 

71.  Potassium  Chromate  and  Potassium  Bichromate  .        .        .  102 

72.  Ammonium  Dichromate 104 

73.  The  Percentage  of  Chromium  in  Ammonium  Dichromate 

(Quantitative) 105 

74.  The  Percentage  of  Iron  in  Ferrous  Ammonium  Sulphate 

(Quantitative)       .........  106 

75.  Determination  of   the  Percentage  of  Chlorine   in  Sodium 

Chloride  (Quantitative) 107 

76.  Analysis  of  a  Silver  Coin  (Quantitative)          ....  109 

77.  The  Atomic  Weight  of  Copper  by  reducing  Cupric  Oxide 

(Quantitative) 110 

78.  Percentage  of  Copper  in  Copper  Sulphate  Crystals  (Quanti- 

tative)    112 

79.  The  Atomic  Weight  of  Copper  by  Oxidizing  Reduced  Copper 

(Quantitative) 112 

80.  The  Atomic  Weight  of  Sulphur  (Quantitative)       .        .        .113 

81.  The  Formula  of  Zinc  Chloride  (Quantitative)         .         .         .114 

82.  Percentage  of  Oxygen  in  Potassium  Chlorate  (Quantitative)  115 

83.  The  Effect  of  Heat  and  of  Acids  on  Carbonates    .        .         .116 

84.  The  Effect  of  Heat  on  a  Carbonate  (Quantitative)          .        .  118 

85.  Boric  Acid  and  Borax 119 

86.  The  Atomic  Weight  of  Magnesium 120 

87.  The  Production  of  a  Double  Salt 123 

APPARATUS  AND  SPECIAL  MATERIALS 125 

CHEMICALS 127 

MINERALS                                                                 ....  129 


LABORATORY  STUDIES  IN  CHEMISTRY 

EXERCISE  1 

GLASS  ROD.     TUBING 

Apparatus.  —  Triangular  file.     Bunsen  burner.     Wing-top.- 
Materials.  —  Glass  rod  and  tubing.     Sugar. 

Method.  —  Glass  rod  or  tubing  can  be  cut  by  making  a  notch  with 
a  file  and  bending  away  from  the  notch. 

A.  Glass  rod.  —  With  a  triangular  file,  make  a  notch  on  a 
piece   of    thin   glass   rod    15    centimeters    (6    in.)   from   the 
end.1     One  sharp  stroke  of  the  file  is  sufficient.     Holding  the 
rod  as  indicated  in  Fig.  1,  endeavor  to  bend  it  away  from  the 
notch,  and  it  will  break  off 

at  that  point.    Cut  off  three 

such    pieces.       Since    the 

ends  of  the  rods  are  jagged 

and  inconvenient  to  handle, 

round   both   ends   of   each 

rod  by  holding   it  in    the 

Bunsen  flame  and  rotating  / 

the    rod    gently.     Support  FIG>  i 

the  rods  by  the  middle  on  , 

your  test-tube  rack  until  they  cool.     (Hot  glassware  or  hot 

apparatus  of  any  kind  must  never  be  laid  on  the  desk  or  put 

away  under  it.) 

B.  Glass  tubing.  —  Cut,  just  as  you  cut  the  glass  rod,  a  piece 
of  glass  tubing  20  cm.  (8  in.)  in  length.     Hold  the  middle  of 
the  piece  of  glass  tubing  in  the  flame,  turning  it  slowly,  and 

1  Rod  not  over  3  millimeters  in  diameter  is  best.    The  use  of  thick 
stirring-rods  is  a  frequent  cause  of  breakage  of  beakers. 

1 


LABORATORY  STUDIES  IN  CHEMISTRY 


when  it  becomes  red-hot,  gently  and  slowly  draw  the  two  por- 
tions apart.  Do  not  twist  the  tubes.  The  pull  must  be  straight. 
Let  the  two  tubes  cool  and  use  them  to  study  the  effect  of 
heat  upon  a  fragment  of  wood  (match-stick)  and  a  little 
sugar. 

Bending  glass  tubing.  —  For  bending,  fit  a  wing-top  on  the 
Bunsen  burner.  Hold  the  tube  so  that  the  flame  heats  as  long 
a  portion  as  possible,  and  rotate  it  so  that  it  is  evenly  heated. 
When  sufficiently  hot,  remove  it  from  the  flame  and  make  the 
bend. 

In  this  way,  bend  a  glass  tube  15  cm.  (6  in.)  long  into  an 
acute  angle  (Fig.  2).  Cut  a  piece  of  glass  tubing  about  25  cm. 

(10  in.)    long    and    bend    it 

twice  at  right  angles  (Fig.  3). 
This  must  be  done  so  that, 
when  the  double  bend  is  laid 
upon  the  table,  every  part  of 
FIG.  3.  it  will  touch  the  surface  of 

the  latter,  or,  in  other  words, 

the  two  limbs  must  be  in  the  same  plane.  Round  the  sharp 
ends  of  the  bent  tube  by  holding  them  a  short  time  in  the 
flame  —  not  long  enough  to  cause  them  to  collapse. 


FIG.  2. 


CAPACITY  OF  LABORATORY  VESSELS  3 

EXERCISE  2 

CAPACITY  OF  LABORATORY  VESSELS 

Apparatus.  —  A  100  cubic  centimeter  cylinder,  graduated  in  cubic 
centimeters.  (Use  the  expression  c.c.  for  cubic  centimeter.)  Large 
and  small  test  tubes.  Evaporating  dish.  Bottle.  Beaker. 

Materials.  —  Rubber  bands. 

Method.  —  The  vessel  is  filled  with  water,  which  is  then  poured  into 
a  graduated  cylinder. 

Measure  5  c.c.  of  water  in  the  graduated  cylinder  and  pour  it 
into  the  small  test  tube.  This  tube  is  6  in.  long  by  f  in.  diam- 
eter. In  metric  measure  it  is  15  cm.  by  1.8  cm.  Mark  the  up- 
per level  of  the  water  by  a  rubber  band  slipped  around  the 
tube.  See  that  the  upper  edge  of  the  band  is  at  the  lower 
meniscus  of  the  water  (Fig.  4).  Memorize  the  appearance  of 
5  c.c.  of  water  so  that  when  you  are  asked  to  take  that  quantity 
of  a  liquid  in  an.  experiment  you  may  have  a  definite  idea  of 
how  much  is  meant.  Add  another  5  c.c.  of  water, 
mark  the  upper  level,  and  memorize  the  appearance  of 
10  c.c.  of  liquid.  Now  fill  the  tube  completely  and 
pour  the  water  into  the  empty  measuring  cylinder. 

The  length  of  the  large  test  tube  is  8  in.   (about 
20  cm.)  and  its  diameter  1  in.  (2.5  cm.).     Repeat  the 
work,  using  the  large  test  tube.     Where  the  capacity     FIG.  4. 
of  a  vessel  is  greater  than  100  c.c.,  determine  it  by 
first  pouring  exactly  100  c.c.  of  water  in  it  and  then  measuring 
the  additional  water  required  to  fill  it. 

Place  first  25  c.c.  and  then  50  c.c.  of*  water  in  the  beaker, 
marking  the  levels.  Then  get  the  total  capacity.  Get  the 
total  capacity  of  your  evaporating  dish  and  one  of  your  bottles. 
Record  the  results. 


4  LABORATORY  STUDIES  IN   CHEMISTRY 

EXERCISE  3 

DENSITY   OF   LIQUIDS 

Apparatus.  —  Trip  scales  and  weights.  100  c.c.  measuring  cylinder 
graduated  in  c.c. 

Materials.  —  Water.  95  per  cent  grain  alcohol.  Saturated  salt 
water. 

Method.  —  A  measured  volume  of  the  liquid  is  weighed. 

Clean  the  cylinder  if  necessary  and  dry  it  carefully  with  a 
towel.  Weigh  it  as  accurately  as  possible  and  record  the 
weight  in  your  notebook.  Count  the  weights  at  least  twice. 

Remove  the  cylinder  from  the  scales  and  place  in  it  20  c.c. 
of  water.  Read  from  the  bottom  of  the  meniscus  (Fig.  5). 

Weigh  the  cylinder  with  the  water.  Get  the  weight  of  the 
water  by  difference,  and  calculate  the  weight  of  1  c.c. 

Is  the  result  exactly  what  you  would  expect  ?  If  not,  what 
is  the  probable  reason  ?  Bearing  in  mind  the  limits  of  accu- 
racy of  the  scale  and  the  cylinder,  how 
exact  would  the  result  be,  provided  that 
the  work  was  done  as  well  as  possible  ? 
Would  the  fourth  decimal  place  have  any 
value  ?  the  third  ?  the  second  ?  Why  ? 

Dry  the  cylinder  inside  and  out.     You 
need   not  weigh  it  again.      Place  in   it 
20  c.c.  of  alcohol  and  get  the  weight  of 
1  c.c.  in  the   same  way.     Look   up   the 
FlG  5  density  of  alcohol  and  see  how  close  your 

result  is  to  the  truth. 

In  the  same  way,  determine  the  weight  of  1  c.c.  of  saturated 
brine.1 

1  The  weight  of  1  c.c.  of  saturated  brine  is  about  1.2  grams. 


20  CC 


SULPHUR,   COPPER  SULPHATE,   AND  MARBLE       5 

EXERCISE  4 

OF  SULPHUR,  COPPER  SULPHATE,  AND 
MARBLE 

Apparatus.  —  Trip  scales.     Graduated  cylinder.     Evaporating  dish. 

Materials.  —  Broken  roll  sulphur,  free  from  dust.  Clean  marble 
chips.  Copper  sulphate  crystals  (commonly  called  bluestone).  Salt. 
Alcohol. 

Method.  —  The  volume  of  a  weighed  portion  of  the  solid  is  obtained 
by  dropping  it  into  water  in  a  graduated  cylinder. 

Weigh  or  counterpoise  the  dish.  Weigh  in  it  exactly  10 
grams  of  fragments  of  sulphur,  free  from  dust.  The  cylinder 
need  not  be  weighed  Place  in  it  exactly  20  c.c.  of  water. 
Incline  the  cylinder  and  carefully  slide  in  the  10  grams  of 
sulphur  The  increase  in  volume  is  the  volume  of  the  sulphur. 
Calculate  the  weight  of  1  c.c.  of  sulphur.  Look  up  the  den- 
sity of  sulphur  and  see  how  nearly  right  you  are. 

Dry  the  wet  sulphur  as  well  as  you  can  on  paper,  and  put  it 
in  the  place  designated  by  the  instructor.  Repeat  the  whole 
experiment,  using  marble  chips  instead  of  sulphur.  Dry  the 
marble  as  well  as  possible  and  place  it  in  the  receptacle  pro- 
vided. 

Since  bluestone  dissolves  in  water,  you  must  use  some  other 
liquid.  Weigh  off  10  grams  of  bluestone,  just  as  you  did  with 
the  others,  but  place  20  c.c.  of  alcohol  in  the  dry  cylinder. 
Otherwise,  the  determination  is  made  in  the  same  way  as  the 
other  two,  Return  the  alcohol  to  the  bottle  and  place  the 
bluestone  in  the  receptacle  provided. 

If  time  permits,  determine  the  density  of  solid  salt  just  as 
you  did  that  of  bluestone,  using  alcohol  because  salt  is  soluble 
in  water.  The  salt  may  be  thrown  into  the  waste  jar.  The 
alcohol  should  be  returned  to  the  bottle. 


6  LABORATORY   STUDIES   IN   CHEMISTRY 

EXERCISE  5 
SULPHUR 

Apparatus.  —  Watch  glass.  Agate  pan.  Lens.  Funnel.  Two 
small  dry  test  tubes. 

Materials.  —  Roll  sulphur.  Powdered  roll  sulphur.  Flowers  of 
sulphur.  Carbon  disulphide.  Filters. 

Method.  —  See  textbook,  pages  4,  5,  6,  and  7. 

CA  UTION :  Carbon  disulphide  is  highly  inflammable.  It  must  not 
be  heated  nor  used  near  aflame. 

Examine  roll  sulphur.  Is  it  brittle  or  malleable?  Dense 
or  light  ?  Rub  a  piece  on  the  coat  sleeve,  and  bring  it  near 
very  small  pieces  of  paper.  What  is  the  result  ?  Does  it  dis- 
solve in  water  ?  (Use  a  small  piece.) 

Examine  flowers  of  sulphur  and  record  its  properties. 

(a)  Place  0.5  c.c.  of  powdered  roll  sulphur  in  a  dry,  small 
test  tube  and  add  2  c.c.  of  carbon  disulphide.      Shake  until 
the  sulphur  dissolves.     Put  the  liquid  into  a  watch  glass  and 
let  it  evaporate  in  a  place  as  far  from  the  flame  as  possible. 
Examine  the  crystals  with  a  lens.     Make  drawings  of  several 
crystals.     These  crystals  are  sulphur.     This  form  of  sulphur 
is  called  a-sulphur.1 

(b)  Have  ready  a  dry  filter  folded  as  though  to  go  into  a  fun- 
nel (Fig.  6)  and  a  pan  of  water.     Half  fill  a  small  dry  test  tube 


FIG.  6. 

with  crushed  roll  sulphur.  Hold  the  tube  with  a  holder  or 
clamp  and  melt  the  sulphur  by  holding  the  tube  above  a  small 
flame  and  turning  it  constantly.  The  melted  sulphur  should 
be  pale  amber-yellow. 

1  a  (Alpha)  =  first  letter  of  Greek  alphabet. 


SULPHUR  7 

Hold  the  filter  by  the  edge  of  the  threefold  portion  and  pour 
the  melted  sulphur  into  it.  Observe  the  crystallization  of  the 
sulphur.  When  crystals  begin  to  form,  across  the  surface,  pour 
out  the  liquid  portion  into  the  pan  of  water.  Unfold  the  filter 
at  once.  Make  drawings  of  several  crystals  as  they  appear 
when  viewed  with  a  lens.  Compare  with  the  form  of  the 
crystals  obtained  in  (a).  Is  the  color  of  the  two  forms  of  sul- 
phur the  same  ?  Are  both  forms  equally  brittle  ? 

The  form  of  sulphur  you  have  just  made  is  called  ^-sulphur.1 
Set  some  of  the  crystals  aside  for  twenty-four  hours,  and  ex- 
plain the  change  which  occurs. 

Examine  the  sulphur  which  has  been  poured  into  the  water. 
Break  a  piece  of  it.  Is  it  brittle  or  soft  ?  Does  it  probably 
consist  of  a-sulphur  or  /3-sulphur? 
Of  which  would  it  consist  if  you 
kept  it  for  a  day  or  two  ? 

(c)  Half  fill  the  same  test  tube 
again  with  crushed  roll  sulphur 
and  melt  cautiously  as  before.  Hold 
the  tube  with  a  holder  or  take 
•the  clamp  from  your  stand.  This 
time  continue  heating,  studying  the 

changes  in  the  color  and  viscosity  (thickness)  of  the  liquid. 
When  the  sulphur  boils,  light  the  vapor  at  the  mouth  of  the 
tube  and  pour  the  liquid  slowly  into  the  pan  of  water,  moving 
the  tube  in  a  circle  around  the  funnel  so  as  to  obtain  a  coiled 
thread  of  sulphur,  rather  than  a  lump  (Fig.  7). 

Examine  the  product.  Is  it  hard  or  soft  ?  Is  it  elastic  ? 
Does  it  resemble  the  product  formed  when  melted  sulphur  was 
poured  into  water  in  (b)  ?  Keep  some  of  the  product  from  (c) 
and  describe  any  change  which  takes  place  in  it.  Is  it  a  stable 
form  of  the  element  ?  Should  you  expect  to  find  it  in  nature  ? 

1  /3  (Beta)  =  second  letter  of  Greek  alphabet. 


8 


LABORATORY   STUDIES   IN   CHEMISTRY 


EXERCISE  6 
GALENITE.     THE   USE   OF   THE   BLOWPIPE 

Apparatus.  —  Blowpipe.  Wing-top  burner.  Funnel.  Small  test 
tube. 

Materials.  —  Asbestos  fiber.  Prismatic  blowpipe-charcoal.  Gale- 
nite  (a  crystallized  specimen  for  examination  and  some  of  the 
crushed  mineral).  Minerals  can  be  crushed  with  a  hammer  upon  a 
heavy  iron  plate.  A  cylinder  of  tin  or  cardboard,  about  8  cm.  high  x 
15  cm.  in  diameter,  open  at  both  ends,  is  convenient  to  prevent  the 
mineral  from  flying  sideways. 

Method.  —  See  textbook,  page  10. 

(a)  Wash  off  the  mouthpiece  of  the  blowpipe.  Close  the 
holes  at  the  base  of  the  burner  and  fit  on  the  wing-top.  Use 
the  luminous  flame  turned  down  to  a  height  of  2.5  cm.  (1  in.). 
Take  the  blowpipe  with  the  right  hand  about 
7.5  cm.  (3  in.)  above  the  bend.  Rest  the 
right  elbow  on  the  table  and  put  the  tip  of 
the  blowpipe  about  halfway  through  the 
flame,  the  broad  surface  of  which  should  be 
toward  you.  Blow  gently.  Keep  the  cheeks* 
somewhat  distended.  Use  them  as  a  reser- 
voir of  air  which  is  replenished  when  neces- 
sary from  the  lungs.  The  natural  tendency 
of  the  cheeks  to  collapse  will  give  sufficient 
blast.  The  flame  should  be  blue,  noiseless, 
and  steady.  A  flickering  or  noisy  flame  in- 
dicates that  the  blast  is  too  strong. 

(&)  Make,  with  your  knife,  a  depression 
about  3  mm.  (0.1  in.)  deep  by  1  cm.  (0.4  in.) 
diameter,  near  one  end  of  the  charcoal.  Place  a  2  mm.  (0.08 
in.)  fragment  of  galenite  in  this  depression  and  direct  the  flame 
upon  it,  holding  the  charcoal  sloping  upward  away  from  the 
flame  at  an  angle  of  about  20°.  The  flame  should  be  in  the 
same  plane  as  the  long  axis  of  the  coal  (Fig.  8).  The  hottest 
part  of  the  flame  is  just  beyond  the  tip  of  the  inner  blue  cone. 


FIG.  8. 


PYRITE  9 

When  the  action  seems  complete,  let  cool,  remove  the  product 
from  the  charcoal,  and  examine.  Is  it  brittle,  like  galenite  ? 
What  is  it  ? 

CAUTION ':  A  void  inhaling  the  red  poisonous  gas  which  escapes  when 
nitric  acid  acts  upon  metals  or  other  substances. 

(c) 1  Place  1  c.c.  of  powdered  galenite  in  a  small  test  tube  and 
add  2  c.c.  of  concentrated  nitric  acid.  Warm  gently  with  a 
small  flame,  not  touching  the  tube,  until  the  mineral  disappears. 
Half  fill  the  tube  with  water.  Plug  up  the  angle  of  a  funnel 
with  asbestos  and  pour  the  liquid  upon  it.  With  the  aid  of 
more  water,  get  all  the  material  in  the  tube  upon  the  asbestos. 
Wash  three  times  with  water  to  remove  nitric  acid.  What  does 
the  residue  appear  to  be  ?  Let  it  dry  as  long  as  time  will  per- 
mit, place  it  on  charcoal,  and  heat  with  the  blowpipe  flame. 
When  it  begins  to  burn,  stop  heating  and  notice  the  odor.  Does 
this  confirm  your  guess  as  to  its  nature  ? 

EXERCISE  7 

PYRITE 

Apparatus.  —  Blowpipe.  Wing-top  burner.  Small  test  tube.  Fun- 
nel. Magnet. 

Materials.  —  Pyrite  (a  well-crystallized  specimen  for  examination 
and  some  of  the  crushed  mineral  for  class  use).  Asbestos.  Prismatic 
blowpipe-charcoal.  Glass  tubing. 

Method.  —  See  textbook,  page  13. 

(a)  Place  a  2  mm.  (0.08  in.)  fragment  of  pyrite  in  a  depression 
on  charcoal  and  heat  it  in  the  same  way  as  the  galenite.  Inter- 
rupt the  heating  from  time  to  time  to  notice  the  odor  produced. 
What  element  is  indicated  by  this  ?  When  the  action  seems 
complete,  break  up  the  residue  and  try  the  action  of  a  magnet 
upon  it.  What  is  the  result  ?  What  metal  is  indicated  ? 

1  During  the  exercises  upon  the  separation  of  sulphur  from  sulphides 
by  nitric  acid,  the  ventilation  of  the  laboratory  may  demand  some 
attention. 


10  LABORATORY   STUDIES   IN   CHEMISTRY 

(6)  Make  a  tube  sealed  at  one  end  (Ex.  1,  B).  Place  in  it 
0.5  c.c.  of  crushed  pyrite  and  heat  it  in  the  flame  of  the  burner, 
after  removing  the  wing-top.  What  element  do  you  detect? 
If  in  doubt,  break  the  tube,  scrape  out  the  substance  in  the  upper 
part  with  a  little  wad  of  asbestos,  burn,  and  notice  the  odor. 

(c)  Treat  1  c.c.  of  powdered  pyrite  with  2  c.c.  of  nitric  acid 
and  carry  out  directions  of  part  (c)  of  the  preceding  exercise 
with  it.  Avoid  inhaling  the  gas  given  off  when  the  nitric  acid 
interacts  with  the  mineral. 

What  element  do  you  detect  ?  What  is  the  color  of  pyrite  ? 
What  is  the  form  of  the  crystals  ?  Make  a  drawing  of  a 
crystal  in  your  notebook.  Is  it  hard  or  soft?  Can  you 
scratch  it  with  a  knife  ? 


EXERCISE  8 
CHALCOPYRITE 

(Copper  Pyrite) 

Apparatus.  —  Blowpipe.  Wing -top  burner.  Magnet.  Funnel. 
Small  test  tube.  Bottle. 

Materials.  —  Chalcopyrite.  Pyrite.  Asbestos.  Prismatic  blow- 
pipe-charcoal. Iron  nails.  Glass  tubing.  • 

Method.  —  See  textbook,  page  14. 

Examine  chalcopyrite  and  compare  it  with  pyrite,  especially 
in  color,  hardness,  and  crystalline  form. 

(a)  Heat  a  2  mm.  (0.08  in.)  fragment  on  charcoal  just  as  you 
did  with  pyrite.     Test  the  residue  with  a  magnet.     What  is 
the  result  ? 

(b)  Carry  out  directions  of  part  (b)  of  Exercise  7  with  chalco- 
pyrite.    What  element  do  you  detect  ? 

(o)  Carry  out  directions  of  part  (c)  of  the  preceding  exercise, 
using  1  c.c.  of  powdered  chalcopyrite  and  2  c.c.  of  concentrated 
nitric  acid.  Receive  the  liquid  which  passes  through  the 
asbestos  in  a  bottle. 


ARTIFICIAL  SULPHUR-COMPOUNDS  11 

Burn  the  solid  which  remains  on  the  asbestos.     What  is  it  ? 

Note  the  color  of  the  liquid  in  the  bottle.  This  color  is 
characteristic  of  copper  compounds  dissolved  in  water.  Dilute 
the  liquid  to  at  least  200  c.c.,  add  four  to  five  drops  of  concen- 
trated sulphuric  acid  and  place  an  iron  nail  or  a  piece  of  zinc 
in  the  liquid.  Describe  the  substance  which  is  deposited. 
What  is  it  ?  What  three  elements  do  you  detect  in  chalco- 
pyrite  ? 

EXERCISE   9 

ARTIFICIAL   SULPHUR-COMPOUNDS 

Apparatus.  —  Small,  dry  test  tube.  Trip  scales.  Asbestos  board. 
Lens.  Medicine  dropper.  Mortar  and  pestle.  Wing-top  burner. 
Blowpipe.  Prismatic  charcoal. 

Materials.  —  Flowers  of  sulphur.  Iron  wire.  Zinc  dust.  Mer- 
cury. Thin  sheet  copper  (0.05  mm.  thick).  Lead  foil  or  test  lead. 

Method.  —  For  copper  sulphide,  see  textbook,  page  18,  section  23. 
For  lead  sulphide,  see  textbook,  page  11.  For  zinc  sulphide,  see  text- 
book, page  17.  For  mercury  sulphide,  see  textbook,  page  16. 

(a)  Cut  a  piece  of  sheet  copper  4  x  12  cm.  (1.6  X  5  in.). 
Weigh  it  on  the  trip  scales.  Fold  it  parallel  to  the  long  diam- 
eter so  that  the  cross  section  forms  a  W  (Fig.  9),  and 
satisfy  yourself  that  it  will  slip  easily  into  a  small,  dry 
test  tube.  Make  a  hole  near  the  edge  of  the  copper  so 
that  you  can  hang  it  from  an  iron  wire. 

Fill  the  test  tube  5  cm.  (2  in.)  deep  with  flowers  of 
sulphur,  clamp  the  tube  near  the  mouth,  and  heat  it 
until  the  sulphur  boils  violently  and  the  tube  is  filled 
with  the  vapor. 

Lower  the  copper  into  the  sulphur  vapor  (not  into  the 
liquid).     Does  there  seem  to  be  any  evolution  of  heat  ? 
When  the  action   is   complete,  withdraw  the   product    FlG  <( 
carefully  and  weigh  it.     Result  ?     Is  the  product  crys- 
talline ?     (Use  a  lens  and,  if  necessary,  examine  results  ob- 
tained by  other  students.)     Does  the  product  resemble  copper 
or  sulphur  in  its  properties?     Proceed  at  once  with  (6). 


12  LABORATORY   STUDIES   IN   CHEMISTRY 

(6)  Introduce  into  the  same  test  tube  a  mass  of  powdered 
lead  (test  lead)  about  equal  in  volume  to  the  sulphur,  or  use 
lead  foil  torn  into  small  pieces,  and  take  about  six  times  the 
weight  of  the  sulphur.  If  you  do  not  know  this,  estimate  it 
from  the  volume,  remembering  that  1  c.c.  of  liquid  sulphur 
weighs  2  grams.  Heat.  Does  the  product  resemble  galenite  ? 
Does  it  behave  like  galenite  when  heated  on  charcoal  before 
the  blowpipe  ?  Try  it. 

(c)  Tear  a  sheet  of  paper  in  halves  and  place  half  of  it  on 
each  side  of  the  trip  scales.     The  paper  on  the  left-hand  pan 
avoids  contact  between  the  substances  weighed  and  the  scales. 
The  paper  in  the  right-hand  pan  counterpoises  that  on  the  left. 
Use  this  method  hereafter  in  weighing  substances  with  the  trip 
scales.     Weigh  off  2  grams  of  zinc  dust  and  1  gram  of  flowers 
of  sulphur. 

Mix  the  sulphur  and  the  zinc  by  putting  them  together  and 
pouring  repeatedly  from  one  paper  to  another.  Transfer  the 
mixture  to  the  asbestos  board  and  ignite  it  with  the  burner 
held  at  arm's  length.  The  action  is  explosive.  The  product 
is  a  compound  of  sulphur  and  zinc  which  has  the  same  com- 
position as  zinc-blende. 

CAUTION ':  Remove  all  rings  while  working  with  mercury.  Do  not 
get  mercury  in  the  sinks. 

(d)  Melt  3  grams  of  sulphur  in  a  small,  dry  test  tube,  add 
1  c.c.  of  mercury  with  a  medicine  dropper,  and  continue  heat- 
ing.    When  the  action  is  over,  allow  to  cool.     The  mass  con- 
sists of  a  compound  of  sulphur  and  mercury  —  called  mercuric 
sulphide  —  which  has  the  same  composition  as  the  mineral  cin- 
nabar.    Powder  the  product  in  a  mortar  and  examine  it. 


SYNTHESIS  OF  COPPER  SULPHIDE  13 

EXERCISE  10 

SYNTHESIS   OF  COPPER   SULPHIDE   (CUPROUS) 
(  Quantitative) 

Apparatus.  —  Porcelain  crucible  and  cover.  Balance.  Pipe-stem 
triangle.  Meter  stick  (one  for  section). 

Materials.  —  Flowers  of  sulphur.  Copper  wire  No.  30  (B.  &  S. 
gauge).  A  meter  of  this  wire  weighs  about  0.5  gram. 

Method.  —  When  copper  wire  is  heated  with  sulphur,  copper  sul- 
phide, CuaS,  is  formed.  Only  the  sulphur  which  combines  with  the 
copper  remains  in  the  crucible.  The  excess  of  sulphur  burns  off. 
See  textbook,  page  21. 

Weigh  the  crucible  without  the  cover.  Coil  2  m.  of  the 
wire  around  your  pencil  into  a  spiral,  place  in  the  crucible,  and 
weigh  again.  Count  the  weights  at  least  three  times  to  avoid 
errors. 

Record  thus :  — 

Crucible  +  copper 

Crucible  empty  

Copper  

Place  about  a  gram  (roughly  weighed)  of  flowers  of  sulphur 
in  the  crucible,  cover,  and  support  on  the  triangle.  Heat  gently 
until  sulphur  no  longer  burns  between  crucible  and  cover ;  then 
heat  intensely  for  five  minutes.  Take  the  burner  in  the  hand 
and  make,  sure  that  the  upper  part  of  the  crucible  where  it  joins 
the  cover  is  thoroughly  heated.  Let  cool  and  weigh,  after  remov- 
ing cover.  Do  not  remove  cover  until  cold. 

Record  thus :  — 

Crucible  +  copper  sulphide 

Crucible  +  copper  

Sulphur  in  copper  sulphide 

Crucible  +  copper  sulphide 

Crucible  empty  

Copper  sulphide  


14  LABORATORY   STUDIES   IN   CHEMISTRY 


weight  of  copper  x  100  =         cent 
weight  copper  sulphide 


Calculate  the  percentage  composition  of  copper  sulphide  thus :  — 
weight  of  copper  x  100 
weight  copper  sulphide 

weight  sulphur  x  100  =        cent  gu,  hur 
weight  copper  sulphide 

How  do  your  results  agree  with  the  composition  calculated 
from  the  formula  Cu2S  ?  See  textbook,  pages  89  and  385. 

Calculate  the  atomic  weight  of  copper,  taking  that  of  sulphur 
as  32.    Since  the  formula  of  your  sulphide  is  Cu2S,  two  atomic 
weights  of  copper  would  combine  with  one  of  sulphur. 
Hence :  — 

Weight  sulphur  :  weight  copper  : :  32  :  2  x, 
x  =  atomic  weight  copper. 

In  these  calculations,  "weight  of  sulphur"  means  the  sul- 
phur which  combines  with  the  copper ;  that  is,  the  increase  in 
weight  after  heating.  The  quantity  of  sulphur  taken  need  not 
be  accurately  weighed,  since  the  excess  of  sulphur  is  driven  off 
as  vapor  and  burns. 

In  this  exercise,  and  in  all  quantitative  work,  the  student 
should  use  the  utmost  care  to  avoid  errors  in  weighing.  Unless 
the  weighings  are  correct  the  work  is  little  better  than  a  waste 
of  time.  The  weights  should  be  counted  at  least  three  times,  and 
the  result  recorded  methodically  at  once. 


CYANIDE   PROCESS  FOR  EXTRACTING  GOLD      15 


EXERCISE  11 

THE   CYANIDE  PROCESS   FOR  EXTRACTING   GOLD 
FROM   ITS   ORES 

Apparatus.  —  300  c.c.  flask  with  solid  rubber  stopper.  Tinner's 
shears.  Glass  rod. 

Materials.  —  Gold  leaf.  Potassium  cyanide.  Sheet  zinc.  (The 
zinc  should  be  cleaned  with  emery  paper  before  using.) 

Method.  —  See  textbook,  page  29. 

CAUTION ' :  Potassium  cyanide  is  intensely  poisonous. 

(a)  Place  1  gram  potassium  cyanide  with  50  c.c  water  in  the 
flask,  insert  the  stopper,  and  dissolve  by  shaking  Introduce 
about  10  sq.  cm.  (1.5  sq.  in.)  of  gold  leaf.  The  gold  leaf  is  best 
picked  up  with  a  wet  glass  rod,  which  is  then  dipped  into  the 
solution  in  the  flask. 

(6)  Insert  the  stopper  and  shake.  At  intervals  remove  the 
stopper  to  admit  oxygen,  which  takes  part  in  the  change. 
Result  ?  What  stage  in  the  cyanide  process  does  this  illustrate  ? 

(c)  When  the  gold  has  disappeared,  add  2  sq  cm.  (0.3  sq.  in.) 
of  freshly  scraped  sheet  zinc,  cut  into  small  pieces,  and  shake 
vigorously.  Result?  Remember  that  finely  divided  gold  is 
dark  and  without  luster.  What  part  of  the  cyanide  process 
does  this  illustrate  ? 


16  LABORATORY   STUDIES   IN   CHEMISTRY 

EXERCISE   12 
THE  EFFECT  OF  HEAT  ON  WOOD  AND  SOFT  COAL 

Apparatus.  —  Dry  test  tubes.  (Since  the  test  tubes  are  to  be  sacri- 
ficed, damaged  ones  are  preferable.) 

Materials.  —  Sawdust  or  fragments  of  wood.  Soft  coal.  Red  and 
blue  litmus  paper. 

Method.  —  See  textbook,  pages  41  and  43. 

(a)  Fill  a  dry  test  tube  2  cm.  (0.8  in.)  deep  with,  sawdust  or 
fragments  of  wood.  Heat  at  first  gently,  then  strongly.  Test 
gases  given  off  as  to  odor,  effect  on  both  kinds  of  litmus  paper, 
and  combustibility.  What  is  left  in  the  tube  ? 

(6)  Repeat  (a),  using  soft  coal  instead  of  sawdust.  Make 
a  comparison  of  the  results  of  (a)  and  (b)  in  your  notes. 

EXERCISE   13 

WOOD   CHARCOAL  AND  ANIMAL  CHARCOAL 
(BONEBLACK) 

Apparatus.  —  Funnel.      Small  test  tube. 

Materials.  —  Wood  charcoal.  Animal  charcoal.  Litmus  solution. 
Lead  foil  (tea  lead).  Filters. 

Method.  —  See  textbook,  pages  41  and  194. 

(a)  Place  a  1  cm.  (0.4  in.)  piece  of  wood  charcoal  in  a  test 
tube  half  full  of  water.  Is  it  lighter  or  heavier  than  water  ? 
Now  wrap  the  charcoal  in  lead  foil  to  sink  it  and  punch  holes 
in  the  foil  with  a  knife  blade  to  admit  the  water.  Put  it  back 
in  the  test  tube  and  boil  five  minutes.  Remove  the  foil  and 
put  the  charcoal  again  in  water.  Result?  Draw  conclusions 
with  respect  to  the  true  and  apparent  specific  gravity  of  char- 
coal. 

(6)  Prepare  a  dilute  solution  of  litmus  by  adding  one  or  two 
drops  of  the  laboratory  solution  to  half  a  test  tube  of  water. 
Add  enough  boneblack  to  fill  the  tube  2  cm.  (0.8  in.)  deep.  Boil 
several  minutes  and  filter.  Fold  the  filter  paper  first  into  a 


HEATING  METALS  IN   THE  AIR  17 

semicircle,  then  into  a  quadrant  (Fig.  6),  and  fit  it  tightly  to 
the  funnel.     Avoid  filling  the  funnel  above  the  filter. 

What  is  the  action  of  boneblack  on  litmus  solution  ?  What 
is  boneblack  used  for  ? 

EXERCISE  14 

HEATING  METALS   IN   THE   AIK 

Apparatus.  —  Pliers  (one  pair  for  class).  Forceps.  Porcelain  cru- 
cible. Pipe-stem  triangle.  Platinum  foil  (one  piece  will  answer  for 
class).  Tinner's  shears.  Meter  stick.  Balance. 

Materials.  —  Sheet  copper  (0.1  to  0.2  mm.  thick).  No.  30  copper 
wire.  Tin  foil.  Iron  powder  (by  alcohol).  Iron  wire.  Zinc  dust. 
Sandpaper. 

Method.  —  See  textbook,  page  49. 

(a)  Cut  two  pieces  of  copper  about  10  cm.  (2  in.)  square. 
Clean  both  pieces  with  sandpaper.  Was  the  copper  tarnished  ? 
Is  it  likely,  then,  that  the  air  acts  upon  copper  ?  If  so,  the 
action  must  be  very  slow,  but  all  chemical  changes  are  greatly 
quickened  by  heat. 

Hold  one  of  the  pieces  of  copper  in  forceps  and  heat  it  as 
hot  as  you  can  without  melting  it.  When  the  product  of  heat- 
ing begins  to  peel  off,  let  the  copper  cool,  place  a  clean  paper 
on  your  desk,  and  tap  the  copper  upon  it  so  as  to  collect  some 
of  the  new  substance.  Clean  the  copper  with  sandpaper  and 
heat  it  again. 

Would  heat  alone,  without  air,  produce  the  change  ?  In 
order  to  answer  this  question,  roll  up  the  second  piece  of 
copper,  squeeze  the  roll  flat  with  the  pliers,  and  fold  over  the 
ends  so  that  air  will  not  get  at  the  inside.  Heat  as  hot  as  you 
can,  without  melting,  for  five  minutes.  Let  cool,  and  compare 
the  outside  of  the  roll  with  the  inside.  Eesult  ? 

(6)  l  Measure  roughly  5  m.  (5.5  yds.)  of  No.  30  copper  wire, 
coil  it  around  a  lead  pencil,  and  place  in  a  porcelain  crucible. 
Weigh  accurately  and  record  the  weight.  Place  the  crucible 

1  (&)»  (c),  (d),  (e),  can  be  distributed  to  different  students. 


18  LABORATORY   STUDIES   IN   CHEMISTRY 

on  a  pipe-stem  triangle  and  heat  gently.  Slowly  increase  the 
heat  until  you  are  using  the  full  power  of  the  burner.  The 
crucible  should  be  just  above  the  tip  of  the  inner  blue  cone  of 
the  flame. 

After  fifteen  minutes,  turn  the  flame  to  one  half  its  full 
height  for  a  minute  (to  prevent  sudden  cooling  and  cracking 
of  the  porcelain)  and  let  the  crucible  cool.  Weigh  accurately. 
Result  ?  What  are  your  conclusions  ? 

(c)  Heat  a  piece  of  tin  foil  5  cm.  (2  in.)  square  as  in  (6).    The 
crucible  with  the  tin  foil  must  be  accurately  weighed.     Stir  from 
time  to  time  with  an  iron  wire,  being  careful  not  to  lose  any- 
thing from  the  crucible.     After  at  least  fifteen  minutes  full 
heat,  cool  gradually  and  weigh  again.     Result  ? 

(d)  2  c.c.  of  iron  powder,  accurately  weighed  with  the  cru- 
cible, are  heated  and  stirred  as  in  (c)  and  then  reweighed. 

(e)  2  c.c.  of  zinc  dust  heated  exactly  as  in  (c). 

(/) T  Take  a  piece  of  platinum  foil  in  the  forceps  and  heat  it 
to  bright  redness  for  two  minutes.  Platinum  belongs  to  the 
class  of  "  noble  metals."  Let  the  platinum  cool  and  notice  the 
absence  of  alteration. 

EXERCISE   15 

THE   COMBUSTION   OF  PHOSPHORUS   IN  AN 
ENCLOSED   VOLUME   OF   AIR 

Apparatus.  —  Bottle.  Agate  pan.  Graduated  cylinder.  Small, 
flat  cork.  Glass  plate  8  cm.  square. 

Materials.  —  Red  phosphorus.  Asbestos  paper.  Wooden  splints. 
Pins. 

Method.  —  Phosphorus  combines  with  the  oxygen  of  the  air  and 
does  not  affect  the  nitrogen. 

Pin  a  piece  of  asbestos  paper  to  the  cork,  place  on  it 
1  c.c.  of  red  phosphorus,  and  float  it  on  water  in  the  agate  pan. 
Ignite  the  phosphorus  and  at  once  invert  over  it  the  bottle. 

1  For  all  students. 


THE  PERCENTAGE   OF  OXYGEN  IN  AIR 


19 


Wait  until  the  white  cloud  of  phosphorus  pentoxide,  P205,  has 
disappeared.  Slip  a  glass  plate  tightly  under  the  mouth  of 
the  bottle  and  remove  it  from  the  pan  without  allowing  any 
air  to  enter.  Set  it  upright  upon  the  desk.  Light  a  splint, 
remove  the  glass  plate,  and  instantly  plunge  the  burning  wood 
into  the  gas.  Pour  the  water  into  a  graduated  cylinder  and 
measure  its  volume.  Get  the  total  volume  of  the  bottle.  Cal- 
culate the  percentage  of  oxygen  in  the  air. 

How  does  the  result  compare  with  the  accurate  figure? 
(See  textbook,  page  57.)  Should  you  expect  an  exact  result 
or  merely  a  rough  approximation  ?  What  are  the  chief  causes 
of  error  in  the  method  ?  Should  you  expect  the  result  to  be 
low  or  high  ?  Why  ? 


EXERCISE  16 
THE   PERCENTAGE   OF   OXYGEN   IN   AIR 

Apparatus  is  shown  in  the  figure  (No.  10).  A  large  test  tube  is 
closed  by  a  doubly  perforated  rubber  stopper  (No.  5).  One  hole  is 
tightly  plugged  with  a  bit  of  thick  glass  rod, 
the  ends  of  which  have  been  rounded  in  the 
flame.  Through  the  other  hole  passes  a  tightly 
fitting  short  piece  of  glass  tubing  which  reaches 
1  cm.  (0.4  in.)  below  the  stopper.  The  lower 
end  of  this  tube  has  been  held  in  the  flame  until 
it  has  melted  sufficiently  to  reduce  the  bore 
about  one  half.  A  rubber  tube  15  cm.  (6  in.) 
long  connects  the  upper  end  of  this  tube  with 
a  funnel  as  shown  in  the  figure.  The  rubber 
tube  is  provided  with  a  Mohr  pinchcock. 

Materials.  —  Dissolve  200  grams  of  potassium 
hydroxide  in  1  liter  of  water.  Add  20  grams 
of  pyrogallol,  which  will  dissolve  instantly  in 
the  liquid.  This  solution  will  serve  for  at  least 
20  students.  It  should  be  kept  in  a  well- 
stoppered  bottle.  Or,  dissolve  10  grams  potassium  hydroxide  in  50 
c.c.  water,  add  1  gram  pyrogallol,  stir,  and  use  at  once.  Rubber  bands. 


20  LABORATORY  STUDIES  IN  CHEMISTRY 

Method.  —  A  solution  of  pyrogallol  absorbs  the  oxygen  from  a  meas- 
ured volume  of  air,  leaving  the  nitrogen. 

CA  UTION :  Potassium  hydroxide  must  not  be  touched  with  the  fingers 
nor  weighed  on  the  bare  balance  pan. 

Remove  the  test  tube  and  take  out  the  glass  rod  from  the 
stopper.  Pour  about  40  c.c.  of  the  solution  just  mentioned  into 
the  funnel.  Open  the  pinchcock  until  the  liquid  has  filled 
the  rubber  tube  and  the  glass  tube  completely.  If  this  is  care- 
fully done,  scarcely  any  of  the  liquid  need  be  allowed  to  run 
out.  The  solution  stains  the  flesh  and  should  not  be  allowed 
to  touch  the  hands.  It  spoils  on  exposure  to  air,  and  the  ex- 
periment should  be  finished  as  promptly  as  possible  after  the 
solution  is  put  into  the  funnel. 

Now  insert  the  stopper  tightly,  and  then  plug  up  the  second 
hole  of  the  stopper  with  the  piece  of  glass  rod.  Open  the 
pinchcock.  A  little  of  the  solution  will  be  forced  into  the 
test  tube  by  the  pressure  of  the  liquid  above,  and,  as  the  oxygen 
disappears,  more  will  enter.  When  the  liquid  stops  flowing 
in,  close  the  pinchcock  and  turn  the  test  tube  upside  down 
several  times  to  absorb  the  last  traces  of  oxygen.  In  doing 
this,  do  not  take  hold  of  the  tube  with  the  hand,  since  this 
would  warm  the  gas  and  give  a  false  result.  Use  a  paper 
holder  or  a  clamp.  Open  the  pinchcock  and  bring  the  inverted 
test  tube  to  such  a  height  that  the  level  of  the  liquid  in  it  and 
the  funnel  are  the  same.  Why  ? 

Close  the  pinchcock,  bring  the  test  tube  back  to  its  original 
position,  and  mark  the  lower  level  of  the  stopper  and  the 
upper  level  of  the  liquid  with  rubber  bands.  Clean  the  appa- 
ratus, and  with  a  graduated  cylinder  measure  the  capacity 
of  the  tube  up  to  the  lower  and  upper  rubber  bands.  The 
first  is  the  volume  of  the  oxygen,  the  second  that  of  the  air. 
What  result  do  you  obtain  for  the  percentage  of  oxygen  in  the 
air  by  volume  ? 

Calculate  thus :  — 

volume  to  lower  band  x  100 


total  volume  to  upper  band 


=  per  cent  oxygen. 


CHEMICAL  NITROGEN 


21 


EXERCISE  17 
CHEMICAL   NITKOGEN 

Apparatus.  —  Small  flask,  with  rubber  stopper,  thistle  tube,  and  de- 
livery tube  for  collecting  over  water  (Fig.  11).  Agate  pan.  Wire 
cutter.  Three  bottles.  Wire  gauze. 

Materials.  —  Sodium  nitrite  (commercial  crystals).  Ammonium 
chloride  (commercial).  Iron  wire  No.  20.  Christmas-tree  candles. 

Method.  —  Nitrogen  escapes  when  a  solution  containing  sodium 
nitrite  and  ammonium  chloride  is  heated  :  — 


2  H2O 


N2. 


NaN02  +  NH4C1  -+  NaCl 

Put  about  10  grams  of  ammonium  chloride  and  the  same 
quantity  of  powdered  sodium  nitrite,  NaN02,  in  a  small  flask, 
and  add  80  c.c.  water.  Set  up  the  apparatus  as  shown  in  Fig. 
11.  Apply  a  gentle  heat,  let  the  gas  escape  for  three  minutes. 
Why?  Collect  three  bottles  of  the  nitrogen  over  water. 
Stop  heating  as  soon  as  the  reaction  begins,  or  it  will  become  too 
violent.  If  the  evolution  of  gas  threatens  to  become  too  ener- 
getic, immerse  the  gen- 
erating flask  for  an 
instant  only  in  a  pan 
of  cold  water,  which 
should  be  in  readiness. 
This  will  immediately 
quiet  it. 

What  are  the  physi- 
cal properties  of  the 
substance  you  have 
prepared  ?  Does  it 
burn?  Does  it  sup- 
port the  combustion  of 
a  candle?  What  is 
the  most  important 

difference  between  this  nitrogen  and  that  you  have  obtained 
from  the  air  (Exercises  15  and  16)  ?     This  nitrogen  is  a  little 
lighter  than  nitrogen  obtained  from  air.     Why  ? 
3 


FIG.  11. 


22  LABORATORY   STUDIES   IN   CHEMISTRY 

EXERCISE   18 

OXYGEN 

{Preliminary  Experiments) 

Apparatus.  —  Hard  glass  test  tube.  Watch  glasses  about  8  cm. 
diameter.  Beaker.  Small  test  tubes.  Lens.  Wire  gauze. 

Materials.  —  Potassium  chlorate.  Manganese  dioxide.  Mercuric 
oxide.  Wooden  splints. 

Method.  —  For  mercuric  oxide,  see  textbook,  page  53.  Potassium 
chlorate,  when  heated,  passes  into  oxygen  and  potassium  chloride  :  — 

KC103  ->  KC1  +  30. 

The  change  takes  place  at  a  lower  temperature  in  the  presence  of 
manganese  dioxide. 

(a)  Shake  up  some  potassium  chlorate  with  cold  water  iu  a 
test  tube.  Pour  off  a  few  drops  of  the  clear  solution  into  a 
watch  glass  which  serves  as  a  cover  for  a  beaker  half  full  of 
hot  water.  The  beaker  is  placed  on  wire  gauze  on  a  ring  of 
the  stand,  and  the  water  is  kept  hot  by  frequent  heating  to  the 
boiling-point.  When  crystals  form,  examine  them  with  a  lens 
or  a  microscope.  While  the  liquid  in  the  watch  glass  is  evapo- 
rating, go  on  with  (6). 

(6)  Heat  2  c.c.  of  potassium  chlorate  in  a  dry,  clean  test 
tube.  Test  the  escaping  gas  with  a  splint  bearing  a  spark. 
Result  ?  What  is  left  in  the  tube  can  only  be  potassium  chlo- 
rate minus  oxygen.  Let  cool,  dissolve  in  water,  and  evaporate 
a  few  drops  to  crystallization  as  in  (a).  Compare  the  crystals 
with  those  obtained  in  (a),  using  a  lens.  They  consist  of 
potassium  chloride. 

(c)  Have  ready  2  c.c.  potassium  chlorate  and  2  c.c.  manga- 
nese dioxide  on  separate  papers.  Place  the  chlorate  in  a  small, 
dry  test  tube,  clamp  in  a  vertical  position,  and  melt  the  chlorate 
by  the  cautious  use  of  a  small  flame.  Avoid  overheating. 
Show  by  the  spark  that  you  have  not  applied  a  high  enough 
temperature  to  drive  off  any  oxygen. 


OXYGEN  23 

Withdraw  the  flame.  At  once  throw  the  manganese  dioxide 
into  the  melted  chlorate  and  test  with  the  spark.  Result  ?  The 
manganese  dioxide  remains  unaltered.  What  effect  has  it  upon 
the  change  of  the  potassium  chlorate  to  potassium  chloride  ? 

CAUTION:  Rings  should  be  removed  from  the  hands  before  begin- 
ning (of),  as  mercury  alloys  with  gold  and  turns  it  white.  Do  not  get 
mercury  into  the  sinks. 

(d)  Heat  2  c  c.  mercuric  oxide  in  a  hard  glass  test  tube. 
Use  the  spark  test.  Result  ?  What  remains  in  the  tube  ? 


EXERCISE   19 1 
OXYGEN 

(Preparation) 

Apparatus.  —  Large  test  tube  with  rubber  stopper  and  delivery 
tube.  Four  glass  plates  8  cm.  square.  Agate  pan.  Iron  spoon. 
Four  wide-mouthed  bottles.  Beaker.  Wire  cutter. 

Materials. — Iron  wire.  Christmas-tree  candles.  Picture  cord. 
Potassium  chlorate.  Manganese  dioxide.  Sulphur.  Red  phosphorus. 
Sand.  Asbestos  paper. 

Method.  —  See  textbook,  pages  54,  55,  and  56. 

(a)  Mix  on  paper  20  c.c.  potassium  chlorate  with  10  c.c.  man- 
ganese dioxide.  Place  the  mixture  in  the  test  tube.  Hold  the 
tube  in  a  horizontal  position  and  tap  it  gently  so  as  to  make 
a  channel  along  the  upper  side  of  the  mass  for  the  escape  of 
gas  —  otherwise  explosions  may  occur.  ^  Clamp  in  a  horizontal 
position  and  tightly  insert  stopper  bearing  delivery  tube,  lead- 
ing to  agate  pan  of  water.  Four  inverted  bottles  rilled  with 
water  (no  air  bubbles)  should  be  ready  in  the  pan. 

Heat  gently,  beginning  at  the  top.  Obtain  a  steady  evolu- 
tion of  gas.  If  the  latter  conies  off  violently,  stop  the  heat 
until  it  moderates.  Keep  the  burner  in  motion  and  do  not 
heat  any  portion  of  the  tube  hot  enough  to  color  the  flame  yellow. 

1  Two  students  working  together. 


24  LABORATORY   STUDIES   IN   CHEMISTRY 

From  time  to  time,  take  out  water  with  a  beaker  from  the  pan 
so  as  to  keep  the  latter  about  half  full.  Bottles  full  of  oxygen 
can  be  covered  under  water  with  a  glass  plate 
and  set  in  the  desk  right  side  up  until  used. 

(6)  In  the  following  experiments,  the  bottles 
should  be  allowed  to  stand  on  the  desk  and  the 
glass  plate  slipped  aside  just  enough  to  allow 
the  admission  of  the  burning  substance,  which 
should  be  held  near,  but  not  touching,  the 
bottom.  The  flame  should  not  be  allowed  to 
come  in  contact  with  the  bottle,  as  it  will  crack 
the  glass. 

Fasten  a  candle  in  a  wire  as  in  Fig.  12,  light 
and  place  in  oxygen.  Keep  the  flame  upper- 
most. Result  ?  Keep  the  bottle  covered.  How  does  the 
flame  differ  from  that  of  a  candle  burning  in  air,  and  why? 
Why  is  it  finally  extinguished  ?  Does  the  candle  seem  to 
burn  more  or  less  rapidly  in  oxygen  than  in  air  ?  If  it  burned 
at  the  same  rate,  how  much  longer  would  it  burn  in  a  closed 
bottle  of  oxygen  than  in  the  same  bottle  filled  with  air  ?  How 
much  greater  is  the  concentration  of  oxygen  in  pure  oxygen 
than  in  air  under  the  same  pressure  ?  Follow  the  same  line  of 
thought  in  interpreting  the  other  three  combustions. 

(c)  Line  a  clean  iron  spoon  with  asbestos  paper,  fill  it  with 
red  phosphorus,  ignite,  and  place  in  oxygen  as  in  (6).    Does  the 
product  seem  to  be  a  solid  or  a  gas  ?     Name  it.     Clean  the 
spoon  for  the  next  experiment  by  heating  it  to  redness  for  two 
minutes.    It  should  be  held  nearly  vertical  during  this  process, 
so  that  the  melted  phosphorus  may  not  run  out.     Then  let  it 
cool  completely  and  reline  it  for  the  next  experiment. 

(d)  Fill  the  clean,  cold  spoon  with  sulphur,  light,  and  place 
in  oxygen  as  in  (c).     Result?     Name  the  product.     Does  it 
seem  to  be  a  solid  or  a  gas  ?     Cautiously  note  the  odor.     Re- 
serve the  sulphur  in  the  spoon  for  (e). 

(e)  Slip  aside  the  cover  of  the  fourth  bottle  of  oxygen  an 
instant  and  throw  in  10  c.c.  of  sand.     Replace  the  cover. 


CARBON  DIOXIDE  25 

Carefully  melt  the  sulphur  left  in  the  spoon  from  (d)  and 
dip  into  it  one  end  of  a  piece  of  iron  picture  cord  25  cm.  (10 
in.)  long.  Ignite  the  sulphur,  and  lower  the  picture  cord  into 
a  bottle  of  oxygen.  Result?  What  was  the  object  of  using 
the  sand?  Of  using  the  sulphur?  Do  not  get  the  sand  into 
the  sinks. 


EXERCISE  20 
CAKBON  DIOXIDE 

(Preliminary  Experiments) 

Apparatus.  —  Deflagrating  spoon.  Trip  scales.  Glass  tube  about 
35  cm.  (14  in.)  by  about  7  mm.  (0.3  in.)  diameter.  Agate  pan.  Glass 
plate.  Three  wide-mouthed  bottles  of  about  400  c.c.  capacity.  Beaker. 

Materials.  —  Limewater.  Charcoal  powder.  Splints.  Christmas- 
tree  candles.  Iron  wire.  Asbestos  fiber.  Alcohol.  Kerosene. 

Method.  —  See  textbook,  pages  98-104. 

(a)  Production  of  carbon  dioxide  by  combustion.  —  Fill  a  def- 
lagrating spoon  with  powdered  charcoal,  heat  the  charcoal  to 
redness,  and  let  it  burn  in  a  covered  bottle.     Test  the  gas  with 
lime  water. 

Hold  a  dry  clean  bottle  over  a  small  gas  flame  for  a  few 
seconds.  What  product  do  you  notice  ?  Apply  the  lime- 
water  test.  What  is  the  second  product  ?  Eepeat  with  a 
candle  flame.  With  burning  wood.  With  the  flame  of  kero- 
sene. Of  alcohol.  (The  last  two  flames  can  be  conveniently 
obtained  by  dipping  a  bunch  of  asbestos  into  the  correspond- 
ing liquid,  placing  it  on  the  base  of  your  stand,  and  setting  fire 
to  it.) 

Draw  conclusions  regarding  the  existence  of  carbon  in  com- 
bustibles and  the  products  of  their  combustion.  State  the 
evidence. 

(b)  Changes  produced  in  air  by  respiration.  —  Place  some  clean 
limewater  in  a  beaker  and  blow  gently  through  it  by  means 


26  LABORATORY   STUDIES   IN   CHEMISTRY 

of  a  glass  tube.  Result  ?  Invert  three  wide-mouthed  bottles 
full  of  water  in  your  agate  pan  and  collect  air  in  the  first 
bottle  from  the  beginning  of  an  expiration.  Withdraw  the 
bottle  from  the  water  by  means  of  a  glass  plate,  slip  the  plate 
aside  an  instant  and  lower  into  the  bottle  a  lighted  candle. 
Does  it  burn  as  long  as  it  would  in  the  same  volume  of  pure 
air  ?  Why  ? 

In  the  second  bottle,  collect  air  from  the  end  of  an  expira- 
tion, using  the  last  portions  of  air  from  the  lungs.  Test  this 
with  a  candle.  Result?  The  result  is  due  partly  to  the 
small  amount  of  oxygen,  and  partly  to  the  large  amount  of 
carbon  dioxide. 

Fill  the  lungs  with  air  and  hold  the  breath  as  long  as  you 
can  without  discomfort.  Collect  the  first  of  the  expiration 
and  test  it  with  a  candle.  Does  the  result  furnish  any  evi- 
dence of  the  diffusion  of  carbon  dioxide  upward,  or  of  oxygen 
downward,  in  the  lungs  ? 

The  body  burns  up  about  220  grams  of  carbon  in  24  hours, 
almost  all  of  which  is  cast  out  through  the  lungs  as  carbon 
dioxide.  Weigh  off  roughly  this  amount  of  charcoal  on  the 
trip  scales  in  order  to  get  an  idea  of  the  quantity.  Of  course 
the  amount  varies  greatly  in  different  people  and  in  the  same 
person  at  different  times.  The  greater  the  activity  and  the 
lower  the  temperature  of  the  surrounding  air,  the  more  active 
the  internal  combustion  becomes. 


PREPARATION  OF  CARBON  DIOXIDE 


27 


EXERCISE  21 

PREPARATION   OF  CARBON   DIOXIDE 

Apparatus.  —  Gas-generating  bottle.  Iron  spoon.  Trip  scales. 
Five  wide-mouthed  bottles.  Small  test  tubes.  Five  glass  plates. 

Materials.  —  Cracked  marble.  Christmas-tree  candles.  Iron  wire 
No.  20.  Magnesium  ribbon.  Limewater.  Litmus  solution. 

Method.  —  Calcium  carbonate  liberates  carbon  dioxide  with  acids 
(See  textbook,  page  321)  :  — 

CO. 


CaCO3  +  2  IIC1  ->  CaCl2  +  H2O 

Use  the  apparatus  shown  in  Fig.  13.  Place  the  gas  bottle 
almost  horizontal  and  slide  enough  broken  marble  into  it  to 
fill  it  when  upright  to  the  depth  of  1  cm. 
(0.4  in.).  If  the  lumps  are  too  large, 
they  can  be  broken  with  a  hammer  on 
an  iron  plate  —  not  in  a  mortar.  Add 
50  c.c.  of  water,  and  then  hydrochloric 
acid,  slowly  through  the  thistle  tube 
until  a  brisk  evolution  of  gas  is  ob- 
tained. Collect  it  by  downward  dis- 
placement in  four  dry  bottles. 

Investigate  the  physical  properties 
of  the  gas.  Has  it  any  odor  or  taste  ? 
If  in  doubt  about  the  last  point,  let 
the  gas  from  the  generator  bubble 
through  a  little  water  in  a  test  tube  and  taste  the  liquid. 
Test  its  solubility  in  water  by  pouring  water  5  cm.  deep  into  a 
bottle  of  the  gas,  covering  tightly  with  the  hand  and  shaking. 
Suction  upon  the  hand  indicates  solution  of  the  gas. 

Lower  a  lighted  candle  into  a  bottle  of  the  gas.  In  order  to 
illustrate  its  high  density,  place  a  lighted  candle  on  your  desk 
and  pour  carbon  dioxide  over  it,  just  as  you  would  pour  water. 
Balance  a  bottle  on  the  platform  scales  and  pour  a  bottle  of 
the  gas  into  it. 

A  few  substances  will  burn  in  the  gas.     Try  an  8  cm.  (3  in.) 


FIG.  13. 


28  LABORATORY   STUDIES   IN   CHEMISTRY 

piece  of  magnesium  ribbon  wrapped  round  the  stem  of  your 
spoon  and  start  burning  in  the  air.  What  is  the  black  sub- 
stance which  is  obtained  along  with  the  magnesium  oxide  ? 

Pass  carbon  dioxide  through  some  limewater  in  a  test  tube 
for  some  time.  Notice  that  the  calcium  carbonate,  which  is 
at  first  precipitated,  finally  redissolves.  Calcium  carbonate 
is  soluble  in  water  containing  carbon  dioxide,  and  this  solution 
is  present  in  many  "  hard  waters." 

Boil  the  liquid,  and  show  that,  when  the  carbon  dioxide  is 
expelled,  the  precipitate  is  again  obtained 

Add  five  drops  of  litmus  solution  to  10  c.c.  of  water  in  a 
test  tube  and  pass  carbon  dioxide  through  the  liquid.  Result? 
The  presence  of  the  water  is  necessary  to  this  change.  Dry 
carbon  dioxide  does  not  affect  litmus.  Boil  the  liquid. 
Result  ? 

EXERCISE  22 

THE  ACTION  OF  CARBON  ON  OXIDES  OF 
METALS 

Apparatus.  —  Hard  glass  test  tube  with  one-hole  rubber  stopper  and 
delivery  tube.  Trip  scales.  Beaker.  Lens. 

Materials.  —  Cupric  oxide  (CuO).  Tin  oxide  (Sn02).  Lead  oxide 
(PbO).  Powdered  charcoal.  Limewater. 

Method.  —  See  textbook,  page  142. 

(a)  Mix  well  on  paper  5  grams  cupric  oxide  with  0.5  gram 
powdered  charcoal.  Cut  a  piece  of  paper  20  x  1  cm.  (8  X  0.4  in.) 
and  crease  it  in  the  middle,  making  a  V-shaped  trough.  Take  up 
some  of  the  mixture  in  the  trough  and,  holding  the  la.tter  in  a 
horizontal  position,  slip  the  tube  over  it.  Upset  the  trough  and 
deposit  the  powder.  Introduce  the  rest  of  the  mixture  in  the 
same  way,  and  use  this  method  hereafter  when  it  is  necessary 
to  get  a  powder  into  a  tube  without  soiling  the  walls. 

Clamp  the  tube  in  a  horizontal  position  and  insert  the  stop- 
per, letting  the  delivery  tube  dip  into  50  c.c.  limewater  in  a 


ARSENOLITE  AND  ARSENIC  29 

beaker  (Fig.  14).     Heat  with  a  flame  kept  in  constant  motion. 

Watch    the    limewater    closely 

and  explain  the  changes  which   *£&&* 

take   place    in    it.      When   the 

action  seems   complete,  remove 

the  limewater  before  the  burner 

Let   cool  completely,   take   out 

the   stopper,  place   the   residue 

in  the  tube  on   paper  and   ex- 

amine, using  a  lens  if  necessary. 

(6)  Repeat,  using  tin  oxide  (5  FlG< 

grams)  and  charcoal  (1  gram). 

(c)  Repeat,    using    lead  oxide    (2    grams)    and    charcoal 
(2  grams).     Employ  a  gentle  heat. 

What  is  the  practical  importance  of  these  results  ? 

If  the  laboratory  period  is  short,  (a),  (6)  and  (c)  can  be  dis- 
tributed and  the  students  encouraged  to  compare  results. 


EXERCISE  23 
ARSENOLITE   (Arsenious  oxide)   AND  ARSENIC 

Apparatus.  —  Lens.  Blowpipe.  Evaporating  dish.  Small  test 
tube. 

Materials.  —  Arsenious  oxide.  Arsenic.  Thin  sheet  copper.  Pris- 
matic charcoal.  Powdered  charcoal.  Glass  tubing.  Filter  paper. 

Method.  —  See  textbook,  page  293,  section  387.     Also  page  332. 

(a)  Arsenious  oxide.  —  Examine  the  substance  and  compare 
it  with  the  element  arsenic.  Heat  a  trace  of  arsenious  oxide  in 
a  tube  sealed  at  one  end.  Examine  the  sublimate  with  a  lens. 
What  is  the  shape  of  the  crystals  ? 

Dissolve  about  0.1  gram  of  arsenious  oxide  by  boiling  it 
gently  in  a  test  tube  with  dilute  hydrochloric  acid.  Dilute  the 
liquid  to  10  c.c. 

Place  a  clean  piece  of  sheet  copper  about  2  cm.  square  in  a 
dish,  fill  the  dish  two  thirds  with  water,  add  about  1  c.c.  of 


30          LABORATORY   STUDIES   IN   CHEMISTRY 

hydrochloric  acid,  and  heat  almost  to  boiling.  Is  there  any 
action  ?  Add  1  c.c.  of  your  arsenic  solution  to  the  liquid,  and 
continue  heating  for  ten  minutes.  The  deposit  on  the  copper 
is  arsenic.  Remove  the  copper,  dry  it  carefully  with  filter 
paper,  roll  it  up,  and  place  it  in  a  glass  tube  sealed  at  one  end. 
Heat  it  gently.  Result  ?  Look  for  a  sublimate  with  a  lens. 

Mix  about  0.1  gram  of  arsenious  oxide  with  twice  its  weight 
of  powdered  charcoal,  and  heat  the  mixture  in  a  glass  tube 
sealed  at  one  end.  Introduce  the  mixture  with  a  paper  trough. 
The  upper  part  of  the  tube  must  be  dean.  Describe  and  ex- 
plain the  result. 

(b)  Arsenic.  —  Heat  a  1  mrn.  fragment  of  arsenic  in  a  glass 
tube  closed  at  one  end.  Does  it  melt  ?  Does  it  vaporize  ? 
The  two  sublimates  (steel-gray  and  black)  are  different  allo- 
tropic  forms  of  arsenic.  Heat  a  fragment  of  arsenic  the  size 
of  the  head  of  a  pin  on  charcoal  with  the  blowpipe  flame.  The 
visible  product  is  arsenious  oxide.  Note  the  odor  of  arsenic 
vapor. 


EXERCISE  24 
CARBON  MONOXIDE1 

Apparatus.  —  Flask,  dropping*  funnel,  and  delivery  tube  connected 
as  shown  in  cut.  Agate  pan.  Three  bottles.  Wire  gauze.  Three 
glass  plates. 

Materials.  —  Formic  acid.  Sulphuric  acid  (concentrated) .  Lime- 
water.  Iron  wire.  Candles. 

Method.  —  Formic  acid,  when  heated  with  sulphuric  acid,  is  con- 
verted into  carbon  monoxide  and  water.  See  textbook,  page  203. 

Set  up  the  apparatus  as  shown  in  cut  (Fig.  15).  Clamp  the 
flask  firmly.  The  flask  contains  concentrated  sulphuric  acid 

This  method  of  making  carbon  monoxide  is  much  safer  and,  in  all 
respects,  better  than  the  one  usually  given  (heating  oxalic  acid  with  sul- 
phuric acid) .  Nevertheless  it  must  be  remembered  that  carbon  monoxide 


CARBON  MONOXIDE 


31 


to  the  depth  of  1  cm,     The  dropping  funnel  is  two  thirds  filled 
with  formic  acid.     Warm  the  sulphuric  acid  gently  with  a 


FIG    15. 


small  flame  and  allow  the  formic  acid  to  drop  slowly  into  it. 
The  equation  is :  — 


CH202 

(Formic  acid) 


->-    CO '    + 

Carbon  monoxide 


H,0. 


The  water  is  retained  by  the  sulphuric  acid. 

Make,  no  attempt  to  ascertain  the  odor  of  the  gas  and  do  not 
allow  it  to  escape  unnecessarily.  Turn  off  the  stopcock  when  you 
wish  to  stop  the  evolution  of  gas. 

Collect  over  water  three  bottles  of  the  gas.  Is  the  gas  soluble 
in  water  ?  Does  it  burn  ?  Does  a  candle  burn  in  an  inverted 
bottle  of  the  gas  ?  Shake  up  some  limewater  in  a  bottle  of 
the  gas.  Result  ?  Remove  the  cover  an  instant,  ignite  the 
gas,  cover,  and  shake  again.  Result?  What  is  the  product 
of  the  combustion  ?  Write  the  equation. 


32  LABORATORY   STUDIES   IN   CHEMISTRY 

EXERCISE   25 
THE  ATOMIC   WEIGHT   OF  TIN 

(Quantitative) 

Apparatus.  —  Small  test  tube.  Glass  rod.  Porcelain  crucible. 
Pipestem  triangle.  Balance. 

Materials.  —  Pure  tin  foil  (free  from  lead1}.     Nitric  acid. 

Method.  —  Tin  passes  into  tin  dioxide  when  treated  with  nitric  acid 
and  heated  (see  textbook,  pages  298  and  299). 

Weigh  a  porcelain  crucible  without  the  cover.  Weigh  in  it 
1  gram  of  pure  tin  foil.  Pour  upon  the  tin  2  c.c.  of  concen- 
trated nitric  acid,  taking  care  to  moisten  every  part  of  the 
metal.  Place  the  crucible  upon  the  pipestem  triangle  on  a 
ring  of  your  stand,  warm  carefully  until  dry,  heat  to  bright 
redness  for  ten  minutes  and  weigh. 

Calculation :  — 

Sn  +  4  HN03  — >-  Sn02  +  2  H20  +  4  N02. 

The  product  in  the  crucible  is  tin  dioxide,  SnO2,  and  the  gain  in 
weight  is  oxygen.  Hence  the  atomic  weight  of  tin  is  found  from  the 
proportion :  — 

Gain  in  weight :  weight  of  tin  : :  32  :  atomic  weight  of  tin. 

1  Supply  houses  have  a  strong  tendency  to  furnish  an  alloy  of  tin  and 
lead  when  pure  tin  foil  is  ordered. 


THE  DISTILLATION  OF  WATER 


33 


EXERCISE  26 
THE   DISTILLATION   OF  WATER 

Apparatus.  —  Flask,  with  rubber  stopper  and  delivery  tube  bent  as 
indicated  in  Figure  16.  Bottle.  Small  test  tube.  Beaker.  Glass 
rod  (thin).  Wire  gauze. 

Materials.  —  Table  salt.  Ammonia  water.  Red  litmus  paper. 
Potassium  permanganate. 

Method.  —  See  textbook,  page  112. 

(a)  Dissolve  3  c.c.  salt  in   50  c.c.  water   in   a  beaker  by 
stirring.     Place  the  liquid  in  the  flask  and  arrange  as  shown 
in   the   figure.     Boil    gently 

until  3  to  5  c.c.  have  col- 
lected in  the  small  test  tube. 
Taste  the  distilled  water. 
Is  it  free  from  salt?  Ex- 
plain. Repeat,  without  tast- 
ing, with  50  c.c.  of  water 
colored  with  a  crystal  of 
potassium  permanganate. 

(b)  In  a  beaker,  add  3  c.c. 
ammonia  water    to    50    c.c. 
water.      Note    the    odor    of 
the  liquid  and  place  a  drop 
of  it  on  red  litmus  paper. 

After  cleaning  the  appa- 
ratus,  distill  the  dilute  am- 
monia  in  the  same  way  as  FIG.  10. 

you  did  the  salt  water.    Note 

the  odor  of  the  distilled  liquid  and  place  a  drop  of  it  on  red 
litmus  paper.     Is  it  free  from  ammonia  ?     Explain. 


34  LABORATORY  STUDIES  IN  CHEMISTRY 

EXERCISE  27 x 
CRYSTALLIZATION 

Apparatus.  —  Wire  gauze.  Evaporating  dish.  Beaker.  Graduated 
cylinder.  Mortar  and  pestle.  Funnel.  Test  tubes.  Trip  scales. 

Materials. — Filters.  Paper.  Saltpeter  (potassium  nitrate).  Blue- 
stone  (copper  sulphate). 

Method.  —  See  textbook,  page  207. 

(a)  Measure  50  c.c.  of  water  into  a  dish.  Make  sure  that 
the  dish  is  dry  on  the  outside,  place  it  on  wire  gauze,  and 
heat  it  to  boiling.  Gradually  add  25  grams  of  potassium 
nitrate,  stirring  constantly  with  a  glass  rod.  Heat  until 
dissolved. 

Filter  the  liquid  into  a  beaker,  wash  the  dish,  and  dry  the 
outside.  The  liquid  which  runs  through  the  filter  is  called  the 
filtrate.  Return  it  to  the  dish  and  boil  away  about  half  of 
the  liquid.  Let  cool.  Collect  the  crystals  on  a  filter  and 
spread  them  out  on  manila  paper  to  dry.  Is  there  reason 
to  think  that  they  are  purer  than  the  original  material  ? 
Why? 

In  each  of  two  test  tubes,  heat  gently  5  grams  of  potassium 
nitrate  with  10  c.c.  water  until  dissolved.  Do  not  boil.  Cool 
one  tube  quickly  by  running  water  over  it.  Let  the  other  cool 
slowly.  Compare  the  two  crops  of  crystals  and  explain  the 
difference. 

(6)  If  time  permits,  repeat  the  whole  experiment,  using 
bluestone,  which  you  have  powdered  in  a  clean  mortar,  instead 
of  saltpeter. 

1  If  the  laboratory  period  is  short,  (a)  and  (&)  can  be  assigned  to  dif- 
ferent groups  of  students. 


SOLUTION  35 

EXERCISE  28 

PREPARATION   OF   CRYSTALLIZED  SODIUM 
CARBONATE 

Apparatus.  —  Evaporating  dish.  Graduated  cylinder.  Trip  scales. 
Glass  rod. 

Material.  —  Anhydrous  sodium  carbonate  (Na2CO3).  Commercial 
calcined  soda  answers  every  purpose. 

Heat  25  grams  calcined  soda  with  60  c.c.  water  in  a  dish, 
stirring  gently.  If  the  liquid  is  not  clear,  filter  it.  Let  cool. 
The  crystals  which  form  are  the  washing  soda  of  the  house- 
hold (Na2C0310  H20).  Compare  them  with  calcined  soda. 
How  could  you  reconvert  them  into  calcined  soda  ? 

EXERCISE  29  * 
SOLUTION   (1) 

Apparatus.  —  (For  each  group.)  Two  beakers  (100  c.c.).  Two 
watch  glasses  suitable  for  covering  them.  Four  small  test  tubes. 
Two  corks  to  fit  small  test  tubes.  Wide-mouthed  bottle.  Graduated 
cylinder.  Mortar  and  pestle.  Two  pieces  wire  gauze. 

Materials. — Distilled  water.  Powdered  rosin.  Copper  sulphate. 
Alcohol. 

Method.  —  See  textbook,  pages  207,  208  and  214. 

(a)  One  member  of  the  group  should  use  distilled  and  the 
other  ordinary  water.  Carefully  compare  the  watch  glasses. 

Clean  a  watch  glass  and  put  a  few  drops  of  distilled  water 
in  it.  Use  the  watch  glass  as  a  cover  for  a  beaker  half  full  of 
water.  Boil  the  water  in  the  beaker  gently  until  the  water  in 
the  watch  glass  has  evaporated.  Meanwhile,  go  on  with  (b) 
and  (c).  If  necessary,  add  more  water  to  the  beaker.  If 
allowed  to  run  dry,  it  will  break.  Examine  the  watch  glass 
and  set  it  aside.  ,--' 

1  Two  students  working  together. 


36  LABORATORY   STUDIES   IN   CHEMISTRY 

With  a  second  watch  glass,  test  ordinary  water  in  the  same 
way,  using  about  the  same  volume. 

(6)  *  Place  1  c.c.  of  powdered  rosin  in  a  test  tube,  cover  with 
water,  and  shake.  Result  ? 

Pour  off  the  water,  cover  the  rosin  with  alcohol,  and  shake. 
Result  ?  Keep  the  liquid. 

Shake  up  some  copper  sulphate  powder  first  with  alcohol 
and  then  with  water.  Explain  the  meaning  of  the  terms 
soluble,  insoluble,  and  solution. 

Pour  the  alcoholic  solution  of  rosin  into  a  bottle  nearly  full 
of  water.  The  resulting  state  of  things  is  called  a  suspension. 
State,  in  parallel  columns,  some  differences  between  solutions 
and  suspensions. 

(c)  Since  a  liquid  can  only  act  at  the  surface  of  a  solid,  the 
more  surface  exposed,  the  more  rapidly  the  solid  dissolves. 
Therefore,  when  a  solution  is  to  be  prepared  quickly,  the  solid 
should  be  powdered. 

Select  two  crystals  of  bluestone  about  1  cm.  (0.4  in.)  in  diam- 
eter and  nearly  equal  in  size.  Have  ready  two  small  test  tubes 
with  corks  to  fit  them.  Powder  one  crystal  finely  in  a  clean 
mortar  and  introduce  the  powder  into  one  of  the  test  tubes. 
Place  the  unpowdered  crystal  in  the  other  test  tube.  Add,  from 
the  graduated  cylinder,  20  c.c.  of  water  to  each  tube.  Take  the 
time  with  a  watch  and  record  it.  Insert  the  corks  and  shake 
both  tubes  gently  until  the  powdered  bluestone  is  completely 
dissolved.  Observe  the  condition  of  the  crystal  and  estimate 
what  fraction  of  it  remains.  Explain. 

1  If  the  laboratory  period  is  short,  one  member  of  the  group  can  per- 
form (&)  while  the  other  carries  out  (c). 


SOLUTION  37 

EXERCISE  30 1 

SOLUTION   (2) 

Apparatus  (for  each  group).  —  Two  beakers  (100  c.c.).  Two  watch 
glasses  suitable  for  covering  them.  Two  small  test  tubes  with  corks. 
Large  test  tube.  Thermometer  reading  to  150°  C.  Graduated  cylin- 
der (100  c.c.).  Trip  scales.  Two  pieces  wire  gauze.  Funnel. 

Materials.  —  Calcium  sulphate  (powder).  Chalk  (powder).  Thread. 
Calcium  chloride  (dry  commercial).  Sal  ammoniac  (commercial). 
Potassium  carbonate  (commercial).  Ether.  Carbon  disulphide. 
Sodium  thiosulphate  (commercial  "hypo").  Distilled  water.  Fil- 
ters. 

Method.  —  See  textbook,  page  214.     Also  page  302,  section  400. 

(a)  One  member  of  the  group  may  take  calcium  sulphate;  the 
other,  chalk.  Compare  the  watch  glasses. 

Place  1  c.c.  of  powdered  calcium  sulphate  in  a  small  test  tube, 
add  10  c.c.  distilled  water,  cork,  and  shake  several  minutes.  Let 
settle,  filter  some  of  the  liquid  into  a  second  clean  test  tube,  and 
test  it  for  dissolved  matter  as  in  Exercise  29,  (a). 

Treat  chalk  in  the  same  way.  Which  is  the  more  soluble  ? 
If  you  had  neglected  to  filter  and  evaporate,  what  conclusion 
would  you  have  formed  about  the  solubility  of  both  substances  ? 
Chalk  is  commonly  spoken  of  as  an  "  insoluble  "  substance.  Is 
there  anything  entirely  insoluble  in  water  ? 

(6)  Clamp  a  test  tube  containing  10  c.c.  of  water  in  a  vertical 
position.  From  a  ring  of  the  stand  hang  a  thermometer  by  a 
piece  of  thread  so  that  the  bulb  is  in  the  water.  Weigh  off 
5  grams  of  dry  calcium  chloride  on  paper. 

Boil  the  water  with  a  small  flame  and  take  the  temperature. 
Add  the  calcium  chloride  and  when  the  solid  is  all  dissolved 
take  the  boiling  point  again.  Result  ? 

(c)  One  member  of  the  group  may  work  with  sal  ammoniac,  and 
the  other  with  potassium  carbonate.  Carefully  compare  results. 

Weigh  25  grams  of  sal  ammoniac  on  the  trip  scales.  Taking 
the  specific  gravity  as  1.5,  calculate  the  volume  of  the  25 

1  Two  students  working  together. 
4 


38  LABORATORY   STUDIES   IN   CHEMISTRY 

grams.  Measure  80  c.c.  of  water  in  the  graduated  cylinder, 
take  the  temperature  of  the  water,  and  add  the  sal  ammoniac. 
Cover  the  cylinder  tightly  with  the  band  and  invert  repeatedly 
until  the  sal  ammoniac  is  all  dissolved.  Take  the  temperature 
of  the  solution  and  read  the  volume. 

Is  the  volume  of  the  solution  equal  to  the  sum  of  the  volumes 
of  the  substances  it  contains?  What  kind  of  a  heat  effect 
occurs  ? 

Repeat  with  25  grams  of  potassium  carbonate  (commercial 
pearlash).  In  the  calculation,  take  the  specific  gravity  of 
potassium  carbonate  as  2. 

(d)  One  student  may  use  ether ;  the  other,  carbon  disulphide. 
Liquids  may  dissolve  each  other. 

CA  UTION:  Ether  and  carbon  disulphide  must  not  be  used  near  a 
flame.  Employ  no  heat  in  these  experiments. 

Place  3  c.c.  carbon  disulphide  in  a  dry,  large  test  tube.  Add 
3  c.c.  water,  one  drop  at  a  time,  shaking  constantly.  Does 
carbon  disulphide  dissolve  water  perceptibly  ? 

Now  fill  the  tube  to  within  5  cm.  of  the  top  with  water,  cork 
and  shake.  Does  water  dissolve  carbon  disulphide  to  any 
large  extent  ? 

Repeat,  using  3  c.c.  of  ether.  Is  water  soluble  in  ether  ? 
Is  ether  soluble  in  water  ? 

(e)  Supersaturated  solutions.  —  Place  a  few  drops  of  water  in 
a  test  tube,  half  fill  the  tube  with  sodium  thiosulphate,  —  called 
"  hypo  "  by  the  photographer,  —  and  heat  with  a  small  flame 
kept  in  constant  motion.    When  complete  solution  has  occurred, 
pour  the  liquid  into  a  clean  tube  and  cover  it  with  paper  to 
exclude  dust.     Let  it  cool.     No  solid  should  separate.     Throw 
into  the  cold  liquid  a  crystal  of   solid  sodium   thiosulphate. 
Result  ?     What  is  a  supersaturated  solution  ?     Do  you  regard 
it  as  a  stable  or  an  unstable  state  of  things?     Would  any 
crystal  answer  the  purpose,  if  dropped  into  the  supersaturated 
solution  in  this  experiment  ?     See  textbook,  pages  209  and  215. 


WATER   OF   CRYSTALLIZATION  39 

EXERCISE  31 
WATER  OF   CRYSTALLIZATION 

Apparatus.  —  Eight  clean,  dry,  small  test  tubes.     Evaporating  dish. 

Materials.  —  Crystals  of  sodium  sulphate.  Copper  sulphate.  Zinc 
sulphate.  Potassium  sulphate.  Calcium  sulphate  (cleavage  pieces  of 
gypsum).  Alum.  Barium  chloride.  Potassium  nitrate.  Alcohol. 

Method. — Water  of  crystallization  is  driven  off  as  steam  when 
crystals  containing  it  are  gently  heated. 

Gently  heat  a  few  crystals  of  each  substance  in  a  dry,  clean 
test  tube.  Use  a  separate  tube  for  each  experiment  and  clamp 
it  in  a  horizontal  position,  so  that  the  water  may  not  run  back 
into  the  hot  portion  and  break  it.  The  flame  should  be  kept 
in  constant  motion,  and  the  heat  should  not  be  intense  enough 
to  color  the  flame  yellow. 

Classify  these  eight  substances  into  (1)  those  which  contain 
water  of  crystallization'  and  (2)  those  which  form  anhydrous 
(water-free)  crystals.  What  change  in  structure  occurs  when 
the  water  is  driven  off  from  the  first  set  ?  Note  that  anhydrous 
crystals  may  contain  traces  of  water  as  an  impurity. 

Attend  especially  to  the  striking  change  in  the  case  of  cop- 
per sulphate.  Dissolve  most  of  the  heated  copper  sulphate 
(it  is  anhydrous  copper  sulphate,  CuS04)  in  the  smallest  pos- 
sible quantity  of  hot  water,  transfer  the  liquid  to  a  dish  and 
let  it  cool.  Explain.  Throw  the  rest  of  the  anhydrous 
copper  sulphate  into  5  c.c.  of  95  per  cent  alcohol.  What 
is  the  result  ?  Remember  that  the  remaining  5  per  cent  of 
the  alcohol  is  chiefly  water.  Suggest  a  test  for  water  based 
upon  this  behavior. 


40  LABORATORY   STUDIES   IN   CHEMISTRY 

EXERCISE  32 

WATER   OF  CRYSTALLIZATION 
(Quantitative) 

Apparatus.  —  Small  porcelain  crucible  without  cover.  Pipestem 
triangle.  Balance. 

Materials.  —  Barium  chloride.  Magnesium  sulphate.  Copper  sul- 
phate. Calcium  sulphate  (coarsely  powdered  gypsum). 

Method.  —  The  water  is  driven  off  by  heat  and  its  quantity  obtained 
from  the  loss  in  weight. 

It  is  convenient  to  assign  the  different  substances  to  different 
groups  of  students. 

Clean  and  dry  the  crucible  and  weigh  it  accurately.  Weigh. 
in  it  exactly  one  gram  of  barium  chloride.  Count  the  weights 
at  least  three  times  to  avoid  errors. 

Record  the  weights  at  once,  thus :  — 

Weight  of  crucible  +  barium  chloride 

Weight  of  crucible,  empty  

Weight  of  barium  chloride  taken  .     '.     '.     '.     '.     ~. 

Adjust  a  ring  of  your  stand  to  the  proper  height  and  support 
the  crucible  on  it  by  means  of  a  pipestem  triangle.  Heat,  at 
first  gently.  After  five  minutes  allow  the  bottom  of  the  cru- 
cible to  come  to  &  faint  red  heat  (no  hotter)  and  maintain  it  at 
that  temperature  for  ten  minutes.  Let  cool  and  weigh  when 
cool  enough  to  handle. 

Record  thus :  — 

Weight  of  crucible  +  barium  chloride  

Weight  of  crucible  +  barium  chloride  (after  heating) 

Loss  in  weight  (water)  

loss  in  weight  x  100 =  per  cent  of  water. 

weight  of  barium  chloride  taken 

The  other  three  substances  are  treated  in  the  same  way  ex- 
cept that  the  temperature  required  is  different. 


THE  ACTION  OF  ZINC  AND  IRON  ON  WATER    41 

Copper  sulphate  should  be  heated  ten  minutes  with  a  half- 
sized  flame  kept  in  motion.  No  part  of  the  crucible  should 
glow.  After  weighing,  the  product  can  be  dissolved  in  the 
crucible  in  the  smallest  possible  quantity  of  hot  water  and 
allowed  to  cool.  Result  ? 

Calcium  sulphate  should  be  heated  gently  for  five  minutes. 
It  should  then  receive  the  highest  temperature  the  burner  will 
yield  for  ten  minutes,  after  which  it  should  be  cooled  gradually 
by  lowering  the  flame  to  half  size  for  a  minute  before  turning 
it  out,  otherwise  the  crucible  may  crack.  Crucibles  which  have 
been  highly  heated  should  always  be  cooled  in  this  way. 

Magnesium  sulphate  should  be  heated  in  the  same  way  as 
calcium  sulphate. 

EXERCISE  33  * 
THE  ACTION   OF   ZINC   AND   IRON   ON  WATER 

Apparatus.  —  Small  test  tube  with  rubber  stopper  and  delivery  tube. 
Medicine  dropper.     Glass  plate.     Bottle.     Agate  pan. 
Materials. — Zinc  dust.     Iron  filings.     Wooden  splints. 
Method.  —  Heated  zinc  dust  or   iron  powder   liberates   hydrogen 

from  steam. 

Zn  +  H20->ZnO  +  H2 

3  Fe  -f  4  H2O  ->  Fe3O4  +  4  H2. 

(a)  Hold  the  tube  vertical  and  let  fall  with  the  medicine 
dropper  10  drops  of  water  to  the  bottom.  Do  not  wet  the  sides. 
Cut  a  slip  of  paper  20  x  1  cm.  (8  x  0.4  in.)  and  fold  it  into  a 
little  V-shaped  trough  which  will  slip  into  the  tube.  Holding 
the  tube  in  an  inclined  position,  put  in  with  the  paper  trough 
enough  zinc  dust  to  soak  up  the  water  completely.  Hold  the 
tube  nearly  horizontal  and  deposit  twice  the  quantity  of  dry 
zinc  dust  at  D  just  above  the  wet  zinc  dust.  Clamp  the  tube 
in  a  horizontal  position  and  insert  the  stopper  with  the  deliv- 
ery tube  leading  to  a  pan  of  water  (Fig.  17). 

1  (a)  and  (6)  can  be  distributed  to  different  students. 


42 


LABORATORY   STUDIES   IN    CHEMISTRY 


Heat  D,  gently  at  first,  then  as  intensely  as  you  can  without 
softening  the  tube,  then  brush  W  with  the  flame  so  as  to  cause 
steam  to  pass  over  the  hot  zinc.  Return  constantly  to  D  with 
the  flame  to  keep  it  heated.  Allow  the  gas  to  escape  for  the 
first  minute.  Why  ?  Then  collect  it  in  an  inverted  bottle  full 
of  water.  When  the  bottle  is  full,  slip  a  glass  plate  under  it 


W      D 


FIG.  17. 


and  remove  it  from  the  water.  Keeping  the  bottle  inverted, 
thrust  a  burning  splint  up  into  the  gas.  Is  the  gas  combusti- 
ble ?  Does  it  support  the  combustion  of  the  wood  ? 

Assuming  that  the  white  substance  formed  in  the  test  tube 
is  a  compound  of  zinc  and  oxygen,  what  conclusion  can  you 
draw  regarding  the  composition  of  water  ?  If  this  explanation 
is  correct,  what  action  should  we  expect  when  iron  is  heated 
with  steam  ? 

(6)  Clean  the  test  tube  and  repeat  the  experiment,  using  iron 
instead  of  zinc. 


THE   INTERACTION  OF  SODIUM  AND  WATER     43 

EXERCISE  34 
THE   INTERACTION  OF   SODIUM  AND  WATER 

Apparatus.  —  Wide-mouthed  bottle.  Beaker.  Watch  glass.  Wire 
gauze.  Small  test  tube.  Agate  pan. 

Materials.  —  Sodium.  Thin  lead  foil  (tea  lead).  Red  and  blue 
litmus  paper.  Phenol  phthalein  solution. 

Method. —  Sodium  liberates  hydrogen  from  water :  — 

Na  +  H20  ->  NaOH  +  H. 

Sodium  must  not  be  touched  with  fingers  which  are  in  the  least  moist 
either  with  water  or  perspiration.  Your  desk  must  be  dry  when  working 
with  it,  and  everything  with  which  you  touch  it  must  be  scrupulously  dry. 
The  air  acts  rapidly  upon  sodium  and  it  must  not  be  exposed.  Take  only 
a  small  piece  from  the  bottle  at  a  time,  and  immediately  cork  the  latter. 
The  liquid  over  the  sodium  in  the  bottle  is  naphtha  or  kerosene,  and  the 
bottle  must  not  be  opened  in  the  vicinity  of  a  flame.  No  sodium  must  be 
put  away  under  the  desk  nor  allowed  to  remain  lying  about,  since  it  may 
catch  Jire.  None  must  be  thrown  into  the  waste  jar,  since  it  may  ignite  the 
paper  or  other  substances  which  the  jar  contains.  Return  any  unused 
portions  to  the  bottle,  or  place  in  a  vessel  specially  provided  for  that 
purpose. 

Throw  a  clean  piece  of  sodium,  free  from  crust,  2  mm.  in  di- 
ameter—  no  larger — into  a  bottle  one  fourth  full  of  water. 
Immediately  cover  the  bottle  with  a  piece  of  paper,  and  wait 
until  the  reaction  is  over  before  removing  the  cover.  The  action 
usually  ends  with  a  slight  explosion  which  may  endanger  the 
eyes  if  the  cover  is  removed  too  soon. 

Describe  what  happens.  Throw  in  another  similar  piece  of 
sodium.  Feel  the  water  in  the  bottle  between  the  fingers. 
Result  ?  Taste  a  little  of  it.  Result  ?  Here,  and  always, 
immediately  reject  the  liquid  tasted  and  rinse  out  the  mouth  with 
water.  Do  not  taste  substances  unless  directed.  Evaporate  a 
few  drops  of  the  liquid  to  dryness  in  a  watch  glass  which 
serves  as  a  cover  for  a  beaker  half  full  of  gently  boiling  water. 
Result?  Try  the  behavior  of  the  liquid  with  red  and  blue 


44  LABORATORY   STUDIES   IN   CHEMISTRY 

litmus  paper,  pieces  about  1  cm.  (0.4  in.)  square  or  less.  Result  ? 
Allow  to  fall  into  the  liquid  a  drop  of  a  solution  of  phenol 
phthalein.  Result  ?  To  what  are  these  new  properties  of  the 
liquid  due  ? 

Wrap  a  clean  piece  of  sodium  2  mm.  (0.08  in.)  in  diameter  in 
dry  lead  foil  (tea  lead).  Punch  several  holes  in  the  lead  with 
a  knife  blade.  Invert  a  test  tube  full  of  water  in  an  agate  pan 
containing  water,  and  quickly  slip  the  lead  containing  the 
sodium  under  it.  If  necessary,  use  another  smaller  piece  of 
sodium  wrapped  in  lead  to  complete  the  filling  of  the  tube. 
Take  no  more  sodium  than  is  directed.  The  use  of  larger 
quantities  is  likely  to  cause  explosions  which  may  imperil  the 
sight. 

What  gas  collects  in  the  tube  ?  Is  it  soluble  in  water  ? 
Does  it  burn  ?  To  what  product  ?  Give  the  evidence  for  the 
belief  that  the  gas  comes  from  the  water,  not  from  the  sodium. 


EXERCISE  35i 
THE   INTERACTION  OF   CALCIUM  AND  WATER 

Apparatus.  —  25  cm.  (10  in.)  glass  tube  open  at  both  ends.  Agate 
pan.  Beaker.  Small  test  tube. 

Materials.  —  Calcium.  Red  and  blue  litmus  paper.  Phenol  phtha- 
lein solution. 

Method.  —  Calcium  liberates  hydrogen  from  water :  — 
Ca  +  2  H2O  ->  Ca(OH)2  +  H2. 

Throw  a  2  mm.  (0.08  in.)  bit  of  calcium  into  50  c.c.  of  water 
in  a  beaker.  Does  gas  escape  ? 

The  liquid  is  lim.eivater,  made  in  an  unusual  way.  How 
does  it  behave  with  red  and  with  blue  litmus  paper  ?  Mix  a 
few  drops  with  a  drop  or  two  of  phenol  phthalein  solution  in  a 
clean  test  tube.  Result  ?  Blow  through  the  remainder  of  the 
limewater  with  the  glass  tube.  Result  ? 
._  Invert  a  test  tube  filled  with  water  in  the  agate  pan  and 

1  Alternative  to  Exercise  34. 


HYDROGEN  45 

place  under  the  mouth  of  the  tube  a  bit  of  calcium.     What 
gas  collects  ?     Is  it  combustible  ? 

NOTE.  —  In  spite  of  the  most  careful  supervision,  accidents  occur 
during  laboratory  work  with  sodium.  The  interaction  of  calcium 
with  water  is  perfectly  safe  and  is  in  all  respects  a  better  experiment. 
Calcium  can  now  be  purchased  quite  cheaply,  though  some  little 
inquiry  may  be  necessary.  The  best  way  to  subdivide  it  is  to  fasten 
in  a  vise  and  chip  it  up  with  a  chisel.  Manual  Training  Schools 
equipped  with  a  "shaper"  can  cut  calcium  into  shavings  which 
answer  perfectly  in  the  laboratory.  Keep  in  tight-stoppered  bottle. 


EXERCISE  36 

HYDROGEN 

Apparatus.  —  Gas-generating  bottle  with  thistle  tube  and  delivery 
tube  for  collecting  over  water.  Agate  pan.  Four  wide-mouthed 
bottles  of  about  400  c.c.  capacity.  Watch  glass.  Beaker.  Small  test 
tubes.  Glass  tubing.  Wire  gauze.  Trip  scales.  Four  glass  plates. 

Materials.  —  Mossy  zinc.  Wooden  splints.  Christmas-tree  candles. 
Iron  wire.  Small  rubber  bands.  Concentrated  sulphuric  acid.  Cop- 
per sulphate  solution.  Copper  oxide  (black).  Filters. 

Method.  —  Zinc  liberates  hydrogen  from  dilute  sulphuric  acid  :  — 

Zn  +  H2SO4->ZnSO4  +  H2. 

(a)1  Place  about  20  grams  of  mossy  zinc  in  a  gas-generating 
bottle.  The  bottle  must  be  held  almost  horizontal  and  the  zinc 
allowed  to  slide  into  it,  otherwise  the  shock  of  the  falling  zinc 
will  break  it.  The  bottle  is  provided  with  a  doubly  perforated 
stopper  carrying  a  thistle  tube  and  a  delivery  tube,  and  the  ap- 
paratus is  arranged  for  collecting  the  gas  over  water. 

Insert  the  stopper  tightly  with  a  twisting  motion,  and  pour 
in  through  the  funnel  tube  enough  water  to  cover  the  zinc. 
The  funnel  tube  must  dip  into  this  water.  Extinguish  any 
burner  flame  that  may  be  in  the  neighborhood,  and  slowly  add 

1  If  the  laboratory  period  is  short,  it  will  be  necessary  to  omit  or  to 
postpone  (6)  and  (c). 


46          LABORATORY   STUDIES   IN   CHEMISTRY 

concentrated  sulphuric  acid  through  the  funnel  tube  until  gas 
is  briskly  evolved.  Do  not  add  too  much  acid.  The  maximum 
should  be  about  one  fourth  as  much  by  volume  as  there  is 
water  present.  Allow  the  gas  to  escape  through  the  water  for 
three  minutes.  Why  ?  Do  not  attempt  at  any  time  in  the  ex- 
periment to  light  the  gas  at  the  exit  tube.  If  the  gas  does  not 
come  off  freely,  add  a  few  drops  of  copper  sulphate  solution 
through  the  funnel  tube. 

Collect  the  gas  over  water  in  wide-mouthed  bottles  of  about 
400  c,c.  capacity.  Determine  its  properties.  Has  it  any  color 
or  odor  ?  Is  it  soluble  in  water  ?  Does  the  method  of  collect- 
ing it  throw  any  light  on  this  last  question?  In  order  to 
obtain  more  definite  information  fill  a  test  tube  half  full  of 
hydrogen  and  mark  the  level  of  the  water  by  a  rubber  band. 
Then  shake  the  tube  for  a  time,  keeping  its  mouth  under 
water.  Result  ?  Use  this  method  hereafter  in  testing  the 
solubility  of  gases. 

Will  the  gas  support  combustion?  Try  it  by  holding  a 
bottleful  mouth  downward  and  introducing  a  lighted  candle 
fastened  on  a  wire.  Keep  the  candle  out  of  contact  with  the 
walls  of  the  cylinder  so  as  not  to  wet  the  wick.  Withdraw 
the  candle  slowly.  Result  ?  Repeat.  In  all  work  with  candles, 
support  the  candle  on  a  wire  so  that  the  flame  is  uppermost. 

Fill  two  bottles  of  the  same  size  with  the  gas.  Support  one 
in  an  inverted  position  in  a  ring  of  your  stand,  the  mouth  not 
touching  the  table.  Place  the  other  upright.  Uncover  them 
at  the  same  moment  and  allow  both  to  remain  uncovered  for 
one  minute.  Now  thrust  a  lighted  splint  into  each  in  turn. 
Draw  conclusions. 

Fill  a  test  tube  over  water  ^  with  air  and  f  with  hydrogen. 
Ignite  the  mixture.  Explain  the  cause  of  this  behavior. 
Why  does  not  the  flame  strike  back  from  gas  jets  along  the 
mains  to  the  gas  works  ?  Would  it  be  safe  to  supply  cities 
with  a  mixture,  of  gas  and  air  by  means  of  pipes  ? 

(6)  Take  off  the  delivery  tube  from  your  gas  bottle  and  sub- 
stitute a  straight  tube  which  runs  to  the  bottom  of  a  dry  test 


FLAME  47 

tube  clamped  in  a  horizontal  position.  In  this  test  tube  is 
1  c.c.  of  copper  oxide  powder.  If  necessary,  add  more  acid 
through  the  funnel  tube.  Wait  at  least  three  minutes  for  the 
air  to  be  expelled,  then  heat  the  copper  oxide.  Note  the  change 
in  the  copper  oxide.  Look  in  the  cooler  part  of  the  tube  for 
the  other  product.  Explain.  What  other  element  most  re- 
sembles hydrogen  in  its  action  on  oxides  ? 

(c)  Filter  a  few  drops  of  the  liquid  which  remains  in  the  gas 
bottle  into  a  watch  glass.  Place  it  on  a  beaker  half  full  of  water, 
support  the  beaker  on  wire  gauze,  and  boil  the  water  gently. 

Describe  in  your  notes  the  crystals  which  separate.  They 
are  called  zinc  sulphate,  and  they  contain  zinc,  sulphur,  and 
oxygen.  Sulphuric  acid  contains  hydrogen,  sulphur,  and  oxy- 
gen, so  that  we  may  describe  the  change  which  takes  place  in 
the  gas-generating  bottle  by  the  statement  that  the  zinc  takes 
the  place  of  the  hydrogen. 

EXERCISE  37 
FLAME 

Apparatus.  —  Platinum  wire.  Wire  gauze.  Sheet  copper  20  cm. 
x  15  cm.  (8  x  6  in.).  Safety  lamp. 

Materials.  —  Wooden  splints.  Pins.  Glass  tubing.  Glass  rod. 
Charcoal.  Candle.  Touch  paper.1  Fine  emery  paper.  Solution 
of  one  part  potassium  dichromate  in  20  parts  water,  to  which  has 
been  added  one  part  sulphuric  acid.  Crayon. 

Method.  —  See  textbook,  pages  122,  123,  and  124. 

(a)  Take  the  chimney  off  the  Bunsen  burner.  Light  the 
gas  at  the  tip  in  the  base.  Extinguish,  replace  the  chimney, 
close  the  air  holes,  and  -light  the  gas.  Do  the  size  and  shape 
of  the  orifice  from  which  the  gas  escapes  affect  the  flame  ? 
Formerly,  when  the  naked  gas  flame  was  much  used  for  light- 
ing, the  determination  of  the  area  and  shape  of  the  orifice 
which  gave  the  best  results  was  an  important  matter. 

1  Dip  strips  of  filter  paper  1  cm.  wide  in  a  cold  saturated  solution  of 
potassium  nitrate.  Hang  up  to  dry  over  a  piece  of  glass  tubing. 


48  LABORATORY   STUDIES   IN   CHEMISTRY 

Turn  the  luminous  flame  down  to  a  height  of  2  cm.  (0.8  in.) 
and  hold  a  piece  of  crayon  in  it  for  a  few  seconds.  Result? 
Open  the  air  holes  and  hold  a  fresh  piece  of  crayon  in  the  blue 
flame  for  the  same  length  of  time.  Result  ? 

Turn  the  blue  flame  to  full  height.  Stand  with  your  back 
to  the  window  and  look  through  the  flame  at  a  dark  back- 
ground, e.g.  the  cover  of  a  black  book.  Make  a  sectional  draw- 
ing of  the  flame  as  it  appears  to  you,  indicating  the  different 
regions.  Do  the  same  with  a  candle  flame. 

The  hottest  part  of  the  blue  flame  of  the  burner  is  level  with 
the  tip  of  the  inner  blue  cone.  Verify  this  by  moving  a 
platinum  wire  around  in  different  regions,  and  noting  where 
it  glows  most  brightly.  Note  also  that  it  is  possible  to  obtain 
light  from  the  blue  flame  by  heating  a  solid  body  in  it.  This 
fact  has  revolutionized  the  methods  of  lighting  by  gas. 

Hold  a  piece  of  glass  rod  about  3  mm.  (0.1  in.)  in  diameter 
horizontally  in  the  hottest  portion  of  the  blue  flame  until  it 
sags  perceptibly.  Note  the  time  required  in  seconds  to  produce 
this  effect.  Let  the  rod  cool,  and  repeat  with  the  luminous 
flame.  Use  a  different  portion  of  the  rod,  and  hold  it  at  about 
the  same  level  in  the  flame  as  with  the  blue.  Which  flame 
appears  to  be  more  satisfactory  as  a  source  of  heat  ? 

Rub  together  two  pieces  of  charcoal  1  cm.  (0.4  in.)  from  the 
open  air  holes  at  the  base  of  the  burner  giving  the  blue  flame. 
Result  ?  Does  this  confirm  your  experiment  with  the  crayon  ? 
Judging  from  this,  what  is  the  direction  of  motion  through  the 
air  holes  ?  Does  gas  escape  or  air  enter  ?  Investigate  this 
further  by  holding  a  piece  of  smouldering  touch  paper  1  cm. 
from  the  air  holes.  A  splint  which  has  just  been  blown  out 
can  be  used  almost  as  well. 

(6)  Polish  a  flat  piece  of  sheet  copper  20  x  15  cm.  (8x6  in.) 
with  fine  emery  paper.  Hold  it  vertically  in  the  center  of  the 
flame  with  one  edge  resting  on  the  burner.  The  time  required 
is  only  a  few  seconds.  Judge  by  the  eye  when  to  remove  it. 

Thrust  another  portion  of  the  copper  horizontally  through 
the  hottest  portion  of  the  flame  for  a  few  seconds.  Examine 


FLAME  49 

the  two  sections  of  the  flame  obtained.  What  is  the  chemical 
nature  of  the  discoloration  on  the  copper  ?  What  difference 
does  the  experiment  indicate  regarding  the  chemical  effects 
which  might  be  expected  in  different  parts  of  the  flame? 
Wet  the  discolored  parts  of  the  copper  with  a  glass  rod  which 
has  been  dipped  into  a  solution  of  potassium  dichromate  con- 
taining sulphuric  acid.  Wash  the  copper  and  dry  it.  Card- 
board or  stiff  paper  can  be  used  instead  of  copper,  but  some 
skill  is  required  to  prevent  ignition. 

Hold  in  the  center  of  the  blue  flame,  1  cm.  above  the  bottom, 
a  glass  tube  open  at  both  ends  inclined  at  an  angle  of  45° 
upward.  Bring  the  flame  of  a  splint  to  the  upper 
end.  Result  ?  Blow  out  a  candle  and  instantly 
apply  a  flame  to  the  little  column  of  smoke.  Result  ? 

Thrust  a  wooden  splint  horizontally  through  the 
blue  flame  of  the  burner  1  cm.  above  the  base.  With- 
draw before  it  takes  fire,  and  examine.  Result? 
Support  a  match  by  a  pin  as  indicated  in  Fig.  18 
and  light  the  blue  flame. 

(c)  Hold  a  piece  of  wire  gauze  horizontal  and  bring     FIG 
it  down  vertically  upon  the  blue  flame.     The  gauze 
should  be  large  enough  to  prevent  the  flame  slipping  around 
the  edge.     Result?     Extinguish  the  flame,  turn  on  the  gas, 
and  light  it  above  the  gauze.     Result  ? 

If  a  miner's  safety  lamp  is  available,  examine  it  and  record 
in  your  notes  the  peculiarity  of  its  construction.  Make  a 
sectional  drawing  of  it. 


50  LABORATORY   STUDIES   IN   CHEMISTRY 

EXERCISE  38 
HYDROGEN   SULPHIDE 

Apparatus.  —  Large  test  tube  with  rubber  stopper  and  delivery  tube 
bent  twice  at  right  angles.  Large  test  tube.  Three  small  test  tubes. 

Materials.  —  Iron  sulphide  in  small  fragments.  Red  and  blue 
litmus  paper.  Solutions  of  mercuric  chloride,  copper  sulphate  and 
arsenious  oxide.  Sheet  copper. 

Method.  —  Many  metallic  sulphides  yield  hydrogen  sulphide  with 
hydrochloric  or  dilute  sulphuric  acid.  (See  textbook,  pages  167,  168, 
169):  — 

FeS  +  2  HC1  ->  FeCl2+H2S. 

CAUTION:  Hydrogen  sulphide  is  poisonous.     Avoid  inhaling  it. 

Place  the  large  test  tube  almost  horizontal  and  carefully 
slide  in  enough  iron  sulphide  to  fill  it  1  cm.  (0.4  in.)  deep. 
Add  water  to  the  depth  of  3  cm.  (1.2  in.)  and  then  hydrochloric 
acid  slowly  until  gas  is  briskly  but  not  violently  evolved. 
Clamp  the  tube  upright  and  insert  the  stopper  bearing  a  deliv- 
ery tube.  Collect  a  dry  test  tube  of  the  gas  by  downward  dry 
displacement.  Light  the  gas  in  the  test  tube,  after  removing 
the  delivery  tube. 

What  are  the  two  products  of  combustion  ?  What  evidence 
have  you  of  the  formation  of  each  ?  What  conclusion  can  you 
draw  with  respect  to  the  composition  of  the  gas  ? 

Hold  a  piece  of  clean  sheet  copper  close  to  the  exit  tube  of 
your  apparatus.  A  silver  coin.  Result  ? 

Nearly  fill  a  large  test  tube  with  water  and  let  the  gas  escape 
through  it  for  several  minutes,  running  the  delivery  tube  to 
the  bottom.  Stop  the  production  of  gas  by  filling  the  generat- 
ing tube  with  water  and  pouring  away  the  liquid.  Use  sepa- 
rate small  portions  of  the  solution  of  hydrogen  sulphide  for 
the  following  experiments.  In  each  case,  place  the  hydrogen 
sulphide  solution  in  a  test  tube  and  add  a  few  drops  of  a  solu- 
tion of  the  substances  mentioned. 

(a)  Copper  sulphate. 

(6)  Mercuric  chloride. 


AMMONIA  51 

(c)  Arsenious  oxide. 

In  (c)  after  noting  the  result,  add  a  few  drops  of  hydrochlo- 
ric acid.  Result  ? 

Taste  a  little  of  the  original  hydrogen  sulphide  solution. 
Investigate  its  action  on  both  kinds  of  litmus  paper. 


EXERCISE  39 
AMMONIA 

Apparatus.  —  Large  test  tube,  with  stopper  and  delivery  tube  bent 
once  at  a  right  angle.  Perforated  square  of  cardboard.  Two  glass 
plates.  Evaporating  dish.  Three  small  test  tubes.  Large  test  tube. 
Two  bottles.  Glass  rod. 

Materials.  —  Glue.  Ammonium  chloride.  Ammonium  sulphate. 
Dry  slaked  lime.  Red  litmus  paper. 

Method.  —  See  textbook,  pages  170,  172,  173. 

A  mixture  of  ammonium  chloride  and  slaked  lime  yields  am- 
monia :  — 

2NH4C1  +  Ca(OH)2->CaCl2  +  2  H2O  +  2NH3. 

(a)  Formation  from   organic   matter.  —  Mix   1   c.c.    of   glue, 
powdered  if  necessary,  with  twice  its  volume  of   dry  slaked 
lime.     Heat  the  mixture  gently  in  a  dry,  small  test  tube.     Do 
not  scorch  the  glue.     Note  the  odor  of  the  gas  given  off  and  its 
effect  upon  red  litmus  paper.     After  testing  with  litmus  hold  a 
glass  rod  wet  with  hydrochloric  acid  in  the  gas.     Almost  any 
organic   matter   containing   nitrogen   will   yield    ammonia    if 
treated  in  this  way.     This  can  serve,  therefore,  as  a  test  for 
nitrogen  in  such  substances. 

(b)  Formation  from  ammonium  salts.  —  Take  1  c.c.  of  ammo- 
nium chloride  in  one  hand  and  an  equal  volume  of  slaked  lime 
in  the  other.     Notice  the  odor  of  each.     Rub  together.     Note 
odor  and  apply  the  same  tests  as  in  (a). 

Repeat  with  ammonium  sulphate  and  slaked  lime. 

(c)  Preparation.  —  Place   enough   ammonium   chloride  on  a 
piece  of  paper  to  fill  your  generating  test  tube  5  cm.  (2  in.) 


52 


LABORATORY   STUDIES   IN   CHEMISTRY 


deep.  Add  an  equal  volume  of  slaked  lime.  Mix  well.  Trans- 
fer to  the  test  tube.  Support  the  latter  in  a  horizontal  position 
as  indicated  in  Fig.  19.  The  delivery  tube  passes  upward 
through  a  perforated  card  or  piece  of  pasteboard  held  by  a  ring 
on  the  upper  part  of  the  stand.  The  tube  should  reach  to  the 
bottom  of  the  inverted  bottle.  Warm  gently.  Use  a  small  flame. 
Avoid  heating  the  wet  portion  of  the  tube,  or  breakage  will  re- 
sult. Collect  a  dry  bottle  and  a  dry  test 
tube  full  of  the  gas.  Test  when  the 
bottle  is  full  by  holding  a  rod  wet  with 
hydrochloric  acid  just  below  the  perfora- 
tion in  the  cardboard.  Slight  fumes  can 
be  disregarded.  A  dense,  white  smoke 
indicates  that  the  bottle  is  full  and 
ammonia  is  escaping.  Place  the  bottle 
mouth  downward  upon  a  glass  plate 
until  you  are  ready  to  use  it.  Keep  the 
generator  for  (d). 

Place  your  test  tube  of  ammonia  with 
the  mouth  under  water  in  a  dish. 
Shake  gently.  Result  ?  Warm  a  clean, 
dry  bottle  by  passing  it  rapidly  through 
the  burner  flame.  Holding  it  in  the 
flame  will  crack  it  at  once.  Place  in 
the  bottle  five  drops  of  concentrated 

hydrochloric  acid  and  run  the  acid  around  the  walls  as  much 
as  possible,  holding  the  bottle  upright  and  keeping  it  covered 
with  a  glass  plate.  Now  bring  it  mouth  to  mouth  with  the 
bottle  of  ammonia  and  remove  both  plates,  keeping  the 
bottles  in  contact.  Invert  the  bottles  several  times,  keeping 
them  mouth  to  mouth.  What  is  the  deposit  ?  Write  the 
equation. 

(cf)  Turn  the  delivery  tube  downward  and  bring  it  just  in 
contact  with  the  surface  of  5  c.c.  of  water  in  a  small  test  tube. 
Pass  in  the  gas  for  five  minutes.  What  is  the  action  of  the 
liquid  on  red  litmus  paper  ?  What  hydroxide  must  it  contain  ? 


FIG.  19. 


NEUTRALIZATION  OF  AMMONIUM  HYDROXIDE    53 

Show  by  the  tests  of  (a)  that  this  hydroxide  is  decomposed 
and  the  ammonia  driven  out,  by  heating  the  liquid. 

Place  5  c.c.  strong  ammonia  water  from  your  stock  bottle  in 
a  small  test  tube  and  clamp  in  an  inclined  position  with  the 
clamp  about  at  the  middle  of  the  tube.  Slip  a  large,  dry  in- 
verted test  tube  over  it.  Boil  gently  one  minute.  Keeping 
the  large  tube  inverted,  plunge  its  mouth  under  water  in  a 
dish.  From  the  result  deduce  conclusions  regarding  (1)  the 
solubility  of  ammonia  in  water,  (2)  the  effect  of  heat  upon  its 
solubility. 

EXERCISE  40 

NEUTRALIZATION   OF   AMMONIUM   HYDROXIDE 
BY  ACIDS 

(Ammonium  /Salts) 

Apparatus.  — 100  c.c.  graduated  cylinder.  Hard  glass  tubing  1  cm. 
or  more  in  diameter.  Pipestem  triangle.  Porcelain  crucible  lid. 
Beaker.  Evaporating  dish.  Glass  rod  (thin).  Triangular  file.  Bottle. 

Materials. — Red  and  blue  litmus  paper.  Ammonium  chloride. 
Ammonium  sulphate.  Ammonium  nitrate.  Concentrated  hydro- 
chloric acid.  Ammonia-water. 

Method.  —See  textbook,  pages  236,  237,  238,  287,  302. 

(a)  Place  in  the  graduated  cylinder  10  c.c.  concentrated 
hydrochloric  acid.  Read  from  the  bottom  of  the  meniscus 
(Fig.  4).  Dilute  to  100  c.c.  with  water  and  stir  well. 
Transfer  20  c.c.  of  this  dilute  acid  to  a.  dry  beaker  and  put 
the  rest  in  a  bottle  in  case  of  need. 

Wash  the  cylinder  and  rinse  it  with  a  few  drops  of  strong 
ammonia.  Dilute  10  c.c.  of  ammonia  to  100  c.c. 

Add  this  dilute  ammonia  gradually  to  the  10  c.c.  of  dilute 
acid.  Stir  gently  with  a  thin  glass  rod.  Remember  that  the 
beaker  is  thin  and  can  be  easily  perforated.  Continually  test 
whether  you  have  added  enough  ammonia,  by  shaking  most 
of  the  liquid  off  the  rod  and  placing  a  very  small  drop  on  red 
5 


54          LABORATORY   STUDIES   IN   CHEMISTRY 

litmus  paper.  Use  the  same  piece  of  paper  for  many  tests. 
When  the  paper  is  turned  blue  (what  does  this  indicate?), 
evaporate  the  liquid  almost  to  dryness  in  a  dish,  using  a  very 
small  flame  toward  the  end.  Let  cool.  What  is  the  residue  ? 
Write  the  equation.  How  does  the  equation  differ  from,  the 
one  which  you  wrote  in  (c)  of  the  preceding  exercise  ? 

(&)  Select  a  piece  of  hard  glass  tubing  (Jena  glass  is  best) 
1  cm.  or  more  in  diameter,  and  cut  a  piece  20  cm.  (8  in.)  long. 
Cut  it  by  making  a  deep  notch  by  sawing  with  a  triangular  file, 
and  bending  away  from  the  notch  over  the  edge  of  the  table. 
Place  1  c.c.  of  ammonium  chloride  in  the  middle  of  the  tube. 
Introduce  the  ammonium  chloride  by  means  of  a  strip  of  paper 
1  cm.  (0.4  in.)  wide  which  is  folded  along  the  center  to  make 
a  V-shaped  trough.  Put  in  each  end  of  the  tube  a  piece  of 
red  and  a  piece  of  blue  litmus  paper.  The  litmus  paper 
should  be  damp.  Clamp  the  tube  nearly  but  not  quite  in  a 
horizontal  position,  putting  the  clamp  1  cm.  from  the  end. 
Heat  the  ammonium  chloride  gently.  Watch  the  litmus  paper 
closely  for  changes,  and  for  reversal  of  any  changes  which  may 
occur.  Does  the  litmus  paper  show  that  the  salt  is  decom- 
posed by  heat  into  ammonia  and  hydrochloric  acid  ?  If  so,  does 
the  sublimate  in  the  tube  prove  that  the  two  gases  must,  for  the 
most  part,  reunite  when  they  reach  the  cooler  part  of  the  tube  ? 

Let  the  glass  tube  cool,  wash  it,  and  return  it. 

(c)  Support  a  porcelain  crucible  lid  on  a  pipestem  triangle. 
Place  on  it  a  fragment  of  ammonium  sulphate  the  size  of  the 
head  of  a  pin,  and  heat.  Result  ?  Repeat  with  ammonium 
nitrate. 


METHANE  55 

EXERCISE  41 
METHANE 

Apparatus.  —  Small  test  tube  with  delivery  tube  for  collecting  over 
water.  Bottle.  Mortar  and  pestle.  Agate  pan.  Glass  plate. 

Materials.  —  Soda  lime.  Anhydrous  sodium  acetate  (can  be  either 
purchased  or  made  by  heating  the  crystallized  salt  in  an  iron  dish 
with  constant  stirring).  Lime  water. 

Method.  —  Methane  is  obtained  when  a  mixture  containing  sodium 
acetate  and  sodium  hydroxide  is  heated :  — 

NaC2H3O2  +  NaOH  -+  Na2CO3  +  CH4 

Fill  the  test  tube  two  thirds  full  with  a  mixture  of  equal  vol- 
umes of  powdered  soda  lime  and  powdered  anhydrous  sodium 
acetate.  Clamp  in  a  horizontal  position.  Tap  the  tube  with 
your  pencil  to  make  the  powder  settle  and  leave  a  channel 
along  the  top  for  the  escape  of  gas.  Heat  gently.  Avoid 
softening  the  glass  by  too  high  a  temperature.  Collect  over 
water. 

Eecord  the  physical  properties  of  the  gas.  Burn  a  bottle  of 
it  and  at  once  apply  the  limewater  test.  What  product  of 
combustion  do  you  detect?  What  other  substance  must  be 
formed  by  the  combustion  of  methane  ? 


56  LABORATORY   STUDIES   IN   CHEMISTRY 

EXERCISE  42 l 
CARBOHYDRATES 

Apparatus.  —  Wire  gauze.  Small  test  tubes.  Beaker.  Graduated 
cylinder.  Thin  glass  rod. 

Materials.  —  Glucose.  Ordinary  sugar.  Molasses.  Starch.  Feh- 
ling's solution  (see  below).  Sodium  carbonate.  Red  litmus  paper. 

Method.  —  Glucose  produces,  with  Fehling's  solution,  a  red  pre- 
cipitate of  cuprous  oxide,  Cu2O. 

(1)  69.28  grams  of  powered  copper  sulphate  (CuS04  5  H20) 
is  dissolved  in  warm  water  and  10  drops  of   sulphuric   acid 
added.     The  solution  is  diluted  to  1  liter  in  a  graduated  flask. 

(2)  350  grams  of  Rochelle  salt  (potassium  sodium  tartrate, 
KNaC4H406)  and  100  grams  of  sodium  hydroxide  are  dissolved 
together  in  water  and  the  solution  diluted  to  about   1   liter. 
This  liquid  must  be  kept  in  a  bottle  with  a  rubber  stopper. 

The  mixture  of  equal  volumes  of  (1)  and  (2)  is  called 
Fehling's  solution.  1  c.c.  of  it  interacts  with  0.005  gram  of 
grape  sugar  (glucose,  C6H1206).  The  two  solutions  should  be 
mixed  just  before  use.  Make  50  c.c.  Fehling's  solution  by 
mixing  25  c.c.  of  each  in  a  graduated  cylinder,  stirring 
thoroughly. 

(a)  In  a  test  tube,  dissolve  about  0.5  c.c.  of  glucose  in  20  c.c. 
water.    Heat  10  c.c.  Fehling's  solution  in  a  beaker  to  gentle  boil- 
ing.    Add  two  or  three  drops  of  the  glucose  solution.    Result  ? 
The  precipitate  is  cuprous  oxide,  Cu.20.     Add  another  drop  of 
the   glucose   solution   and  boil  again.     Continue  in  this  way 
until  the  liquid  over  the  precipitate  has  become  colorless.     The 
precipitate  will  remain  red.     Be  careful  to  add  no  more  glucose 
solution  than  is  necessary.     What  weight  of  glucose  have  you 
added  ? 

(b)  Dissolve  about  0.5  c.c.  cane  sugar  in  20  c.c.  of  water  in  a 
beaker.     Add  a  drop  or  two  of  this  solution  to  5  c.c.  Fehling's 
solution  and  heat  in  a  test  tube.     Is  there  any  result  ? 

1  The  discussion  of  carbohydrates  in  textbook,  Chapter  15,  page  191, 
should  be  read  before  this  exercise  is  carried  out. 


ACETIC  ACID,  WOOD  ALCOHOL,  ACETYLENE     57 

To  the  rest  of  the  sugar  solution,  add  10  drops  concentrated 
hydrochloric  acid  and  heat  on  wire  gauze  for  ten  minutes  to 
gentle  boiling.  As  the  water  evaporates,  add  enough  water  to 
keep  the  volume  at  about  20  c.c.  Cool  and  add  solid  sodium 
carbonate  until  a  drop  of  the  liquid  makes  a  blue  spot  on  red 
litmus  paper.  Then  test  with  Fehling's  solution  in  the  same 
way  as  before.  What  does  the  result  show  about  the  action  of 
acids  on  cane  sugar  ?  Would  acetic  acid  have  produced  the 
effect  as  rapidly  as  hydrochloric  ?  Why  ?  The  effect  is  due 
entirely  to  the  H  ions. 

(c)  Boil  0.5  c.c.  of  starch  powder  with  20  c.c.  of  water  and 
repeat  (6)  w'ith  the  starch   solution.     What  is  the  action  of 
dilute  acids  on  starch  ?     What  practical  application  is  made 
of  the  fact  ?     Why,  in  actual  manufacture,  is  it  sufficient  to 
neutralize  the  hydrochloric  acid  with  sodium  carbonate,  instead 
of  removing  it  from  the  sirup  (see  textbook,  page  193).     Why 
does  hydrochloric  acid  act  on  the  starch  more  rapidly  than  most 
other  acids  ?     The  effect  is  due  entirely  to  the  H  ions. 

(d)  Test  a  solution  of  0.5  c.c.  molasses  in  20  c.c.  water  for 
glucose. 

EXERCISE  43 
ACETIC   ACID,  WOOD  ALCOHOL,   ACETYLENE 

Apparatus.  —  Small  test  tubes.     Bottle.     Evaporating  dish. 

Materials.  —  Acetic  acid.  Sodium  acetate.  Iron  filings.  Zinc 
dust.  Magnesium  ribbon.  Alcohol.  Concentrated  sulphuric  acid, 
lied  and  blue  litmus  paper.  Wood  alcohol.  Asbestos  fiber.  Copper 
wire  No.  20.  Iron  wire.  Limewater.  Calcium  carbide. 

Method.  —  See  textbook,  pages  183,  201,  202,  353. 

(a)  Take  10  c.c.  of  acetic  acid  in  a  small  test  tube.  Record 
its  physical  properties.  Note  the  odor.  Does  it  resemble  that 
of  any  common  substance  ?  Add  a  few  drops  to  a  test  tube 
full  of  water.  Taste  the  dilute  acid  and  test  it  with  red  and 
blue  litmus  paper.  Place  in  one  small  test  tube  1  c.c.  of  zinc 
dust,  in  another,  the  same  volume  of  iron  filings,  and  in  a  third, 


58          LABORATORY    STUDIES   IN   CHEMISTRY 

a  spiral  made  of  4  cin.  of  magnesium  ribbon.  Cover  the  metals 
with  concentrated  acetic  acid.  If  necessary,  heat  very  gently 
—  not  to  boiling  —  with  a  small  flame.  What  gas  would  you 
expect  to  obtain?  Is  the  change  rapid  and  violent  or  slow 
and  moderate  ? 

Acetic  acid  is  an  inactive  acid.  Compare  its  activity  with 
that  of  an  active  acid  (sulphuric),  thus :  Dilute  1  c.c.  of  acetic 
acid  with  4  c.c.  of  water.  In  another  tube,  place  4  c.c.  of  water 
and  add  1  c.c.  of  sulphuric  acid.  Add  1  c.c.  of  zinc  dust  to 
each  and  compare  the  behavior.  The  same  kind  of  chemical 
process  occurs  in  both  tubes.  The  main  difference  is  in  the 
speed. 

(6)  Place  1  c.c.  of  sodium  acetate  in  a  test  tube,  add  2  c.c. 
of  water  and  1  c.c.  of  concentrated  sulphuric  acid.  Warm 
gently.  Odor  ?  Effect  on  blue  litmus  paper  ?  In  this  experi- 
ment, sulphuric  acid  produces  acetic  acid  by  interacting  with 
sodium  acetate. 

(c)  To  1  c.c.  of  sodium  acetate  in  a  test  tube  add  2  c.c. 
alcohol  and  1  c.c.  concentrated  sulphuric  acid.    Warm  gently  for 
an  instant  —  not  to  boiling.    (Care  !)    Odor  ?    The  fragrant  sub- 
stance is  called  acetic  ester.    It  has  some  important  applications ; 
for  instance,  in  the  manufacture  of  smokeless  powder  from 
guncotton.     Its  formation,  in  the  way  you  have  just  carried 
out,  serves  as  a  test  for  acetic  acid  or  an  acetate. 

(d)  Wood    alcohol    and    formaldehyde.  —  Note    the   odor    of 
wood  alcohol  and  compare  it  with  that  of  grain  alcohol.     The 
odor  is  due  to  acetone,  an  impurity  which  is  always  present  in 
commercial  wood  alcohol. 

Dip  a  mass  of  asbestos  1  cm.  (0.4  in.)  in  diameter  into  wood 
alcohol,  place  it  on  the  base  of  your  stand  and  set  fire  to  it. 
Hold  over  the  flame  a  dry,  cold,  clean  bottle.  One  product  of 
the  combustion  condenses  on  the  walls.  What  is  it  ?  To  iden- 
tify the  other  product,  pour  at  once  into  the  bottle  5  c.c.  of 
limewater,  cover  with  the  band  and  shake.  Result? 

Formaldehyde  results  from  the  imperfect  combustion  of 
wood  alcohol.  Make  a  spiral  by  wrapping  30  cm,  of  No.  20 


CHLORINE  59 

copper  wire  around  a  lead  pencil.  Heat  the  spiral  red  hot, 
holding  it  with  iron  wire  and  hold  it  close  to  the  surface  of 
2  c.c.  of  wood  alcohol  in  a  small  test  tube.  The  sharp  odor  is 
due  to  formaldehyde. 

(e)  Acetylene. 

Fill  a  small  test  tube  completely  with  water,  cover  tightly 
with  the  thumb,  and  invert  it  in  an  evaporating  dish  full  of 
water.  Slip  under  the  mouth  of  the  tube  a  5  mm.  (0.2  in.)  bit 
of  calcium  carbide.  If  necessary,  use  another  bit  to  complete 
the  filling  of  the  tube. 

The  solid  product  in  the  dish  is  slaked  lime  (calcium  hydrox- 
ide). Test  it  with  litmus  paper  (both  kinds). 

Remove  the  test  tube  from  the  dish,  using  the  thumb,  and 
burn  the  gas.  At  once  pour  into  the  tube  5  c.c.  of  limewater, 
cover  with  the  thumb,  and  shake.  What  product  of  combus- 
tion do  you  detect  ? 

EXERCISE  44 
CHLORINE1 

Apparatus.  —  A  300  c.c.  flask  with  doubly  perforated  rubber 
stopper,  carrying  a  dropping  funnel  and  a  delivery  tube  bent  twice 
at  right  angles  (Fig.  20).  Kipp  hydrogen  generator  (one  will  serve 
for  the  class) .  Four  bottles.  Small  test  tube  with  cork.  Wire  gauze. 
Glass  rod.  Four  glass  plates.  Iron  spoon. 

Materials.  —  Potassium  permanganate  (commercial).  Charcoal. 
Red  and  blue  litmus  paper.  Colored  calico  or  other  cotton  fabric. 
Fresh  slaked  lime.  Ink.  Christmas-tree  candles.  Iron  wire  No.  20. 

Method.  —See  textbook,  pages  212,  213,  220. 

Carry  out  this  experiment  under  the  hood.  Avoid  inhaling  the  gas. 
Be  sure  that  the  cork  of  the  apparatus  Jits  tightly.  If  the  throat  becomes 

1  This  exercise  is  given  because  it  is  included  in  the  syllabi  of  College 
Entrance  Requirements.  It  may  be  dangerous  in  unskilled  hands,  and 
it  is  certain  to  cause  great  discomfort  to  the  students.  Many  teachers 
will  prefer  to  show  it  on  the  lecture  table.  However,  the  production  of 
the  gas  is  under  perfect  control  and  the  method  is  greatly  superior  to  the 
use  of  manganese  dioxide  and  hydrochloric  acid. 


60 


LABORATORY    STUDIES   IN    CHEMISTRY 


irritated,  place  some  alcohol  in  a  beaker  or  on  a  handkerchief  and  inhale 
the  vapor. 

If  hoods  are  not  available,  this  work  should  be  omitted  or  done  at  a  time 
when  the  windows  of  the  laboratory  can  be  open.  A  little  ammonia 
sprinkled  on  the  Jloor  will  reduce  annoyance  from  chlorine. 

Place  crystals  of  potassium  permanganate  1  cm.  deep  in  the 
flask.  The  substance  need  not  be  pure.  Fit  the  flask  with 
a  rubber  stopper  carrying  a  dropping  funnel  and  a  delivery 

tube.  Support  it  firmly  on 
wire  gauze,  and  put  a  small 
flame  8  cm.  below  it.  Allow 
hydrochloric  acid  to  fall  drop 
by  drop  into  the  flask.  Collect 
by  downward  displacement 
one  small  test  tube  and  four 
bottles  full  of  the  gas.  Judge 
when  the  vessel  is  full  by  the 
color,  and  immediately  cover  it 
tightly  with  a  glass  plate  and 
substitute  another ;  otherwise 
the  excess  of  chlorine  will  be 
forced  out  at  the  top  and  make 
the  air  unfit  to  breathe.  Test 
FIG.  20.  tubes  full  of  chlorine  can  be 

corked.     The  exit  tube  of  the 

chlorine  apparatus  must  reach  to  the  bottom  of  the  vessel.  This 
tube  should  be  cut  about  a  foot  from  the  desk  and  united  again 
by  a  short  piece  of  rubber  tube,  that  it  may  be  moved  without 
disturbing  the  apparatus.  The  vessel  in  which  you  are  collect- 
ing chlorine  should  be  kept  covered,  and  the  exit  tube  slipped 
between  the  cover  and  the  side  of  the  bottle.  The  bottles  of 
chlorine  must  be  kept  covered  during  all  experiments.  When 
you  have  finished  and  desire  to  get  rid  of  the  chlorine,  place 
the  bottles  under  the  hood,  remove  the  covers  without  breathing, 
and  at  once  retire  to  a  distance.  After  the  chlorine  has  escaped 
—  which  will  require  ten  minutes  —  the  bottles  can  be  cleaned. 


CHLORINE  61 

Record  the  physical  properties  of  the  element.  Invert  a 
test  tube  full  in  water  and  shake  gently.  Is  it  soluble  ? 

Lower l  a  hydrogen  flame  into  a  bottle  of  chlorine.  If  you 
use  a  gas-generating  bottle  in  this  experiment,  remember  that 
it  must  be  allowed  to  run  five  minutes  and  that  the  generator 
and  stopper  must  be  wrapped  in  a  towel  before  lighting  the 
hydrogen.  Describe  the  appearance  of  the  flame  of  hydrogen 
burning  in  chlorine.  Hold  a  glass  rod  wet  with  ammonia  near 
an  open  bottle  of  hydrochloric  acid.  Result?  This  is  a  test 
for  hydrochloric  acid.  Now  hold  a  rod  wet  with  ammonia  in 
the  gas  left  in  the  jar  in  which  the  hydrogen  was  burned.  Is 
it  hydrochloric  acid  ?  Has  it  the  color  of  chlorine  ?  Heat  a 
piece  of  charcoal  in  a  spoon  until  it  begins  to  burn,  and  place 
it  in  chlorine.  Result?  Keep  the  bottle  covered. 

Take  out  the  charcoal  and  lower  a  lighted  candle  supported 
on  a  wire  into  the  same  bottle  of  chlorine.  The  candle  is  com- 
posed chiefly  of  compounds  of  hydrogen  and  carbon.  The 
black  substance  thrown  off  from  the  flame  is  carbon  (soot). 
Use  the  two  preceding  results  to  explain  this  one.  What  else 
must  be  produced?  Let  the  covered  jar  stand  till  the  soot  set- 
tles and  try  the  test  with  the  glass  rod  wet  with  ammonia. 

In  the  third  bottle,  place  a  bit  of  red  litmus  paper,  a  piece 
of  blue  litmus  paper,  a  strip  of  colored  calico,  and  a  fragment 
of  printed  matter  smeared  over  with  writing  ink  until  it  is 
illegible.  Describe  and  explain  the  results.  What  is  the  most 
important  use  of  chlorine  ? 

In  the  fourth  bottle,  place  some  fresh  slaked  lime  (milk  of 
lime  answers  well),  and  immediately  cover  the  bottle  tightly 
with  the  palm  of  the  hand  and  shake  it'.  Result  ?  Does  the 
chlorine  disappear  ? 

Carefully  add  nitric  acid,  a  few  drops  at  a  time,  to  the  con- 
tents of  the  bottle.  What  happens?  What  very  important 
technical  process  does  this  illustrate  ?  See  textbook,  page  317. 


1  Many  teachers  will  prefer  to  omit  this  experiment  or  to  show  it  on 
the  lecture  table. 


62  LABORATORY  STUDIES  IN  CHEMISTRY 

EXERCISE  45 
THE  ACTION  OF  SULPHURIC  ACID  ON  CHLORIDES 

Apparatus.  —  Four  small  test  tubes.     Glass  rod. 
Materials.  —  Sodium  chloride.     Potassium  chloride.     Ammonium 
chloride.     Barium  chloride.     Red  and  blue  litmus  paper. 
Method.  —  See  textbook,  page  222. 

Place  1  c.c.  of  sodium  chloride  in  a  small  test  tube.  Do  the 
same  with  the  other  chlorides,  using  a  different  tube  for  each. 
Drop  into  each  tube  1  c.c.  of  concentrated  sulphuric  acid. 

To  show  the  behavior  of  water  vapor  with  the  gas  given  off, 
blow  across  the  mouth  of  the  tube.  Ascertain  its  reaction  with 
ammonia  by  holding  a  glass  rod  wet  with  this  substance  in  the 
tube.  Remember,  however,  that  any  add  vapor  or  gas  will 
give  a  white  cloud  with  ammonia.  In  writing  the  equation 
remember,  also,  that  it  is  the  gas  (NH3)  given  off  by  the 
ammonia,  and  not  the  dissolved  substance,  which  combines 
with  the  hydrochloric  acid. 

Hold  in  each  tube  1  sq.  cm.  of  red  and  of  blue  litmus  paper. 
Result  ? 


THE  ACTION  OF  SULPHURIC  ACID  ON  SALT      63 

EXERCISE  46 
THE  ACTION  OF  SULPHUEIC  ACID  ON  SALT 

Apparatus.  —  300  c.c.  flask,  with  singly  perforated  rubber  stopper 
and  delivery  tube  bent  twice  at  right  angles.  Beaker.  Two  small, 
dry  test  tubes.  Three  dry  bottles.  Agate  pan.  Glass  rod.  Wire 
gauze. 

Materials.  —  Table  salt.     Red  and  blue  litmus  paper.    Christmas- 
tree  candles.     Iron  wire.     Filter  paper. 
Method.  —  See  textbook,  page  223. 

Note  the  equation  :  — 


NaCl  +  H2SO4^±  NaHSO4  +  HC1. 

Place  about  25  c.c.  of  water  in  a  beaker.  Stand  the  beaker 
in  a  pan  of  cold  water  and  slowly  pour  in  50  c.c.  concentrated 
sulphuric  acid,  stirring  constantly.  Cool  completely  and  pour 
the  liquid  upon  30  grams  of  salt  in  the  flask. 

Place  the  flask  on  wire  gauze  and  apply  a  gentle  heat. 
Collect,  by  downward  displacement,  two  test  tubes  and  three 
bottles  of  hydrogen  chloride.  The  delivery  tube  must  reach 
to  the  bottom  of  the  bottle,  and  the  bottle  and  delivery  tube 
must  be  dry.  Why  ? 

Is  hydrogen  chloride  soluble  in  water  ?  Try  it  by  placing  a 
test  tube  full  with  its  mouth  downward  in  water.  Does  the 
gas  burn?  Try  with  a  test  tube  full.  Does  it  support  the 
combustion  of  a  candle  ?  How  does  it  affect  red  and  blue 
litmus  paper  ? 

Pour  some  ammonia  011  a  wad  of  filter  paper  and  throw  it 
into  a  bottle  of  hydrogen  chloride.  Result  ? 


64  LABORATORY   STUDIES   IN   CHEMISTRY 

EXERCISE  47 

THE  ACTION  OF  HYDROCHLORIC  ACID  ON  SODIUM 
HYDROGEN  SULPHATE 

Apparatus.  —  Small  test  tube.     Lens. 

Material.  —  Sodium  hydrogen  sulphate,  NatISO4. 

Method.  —  See  textbook,  page  222. 

Make  5  c.c.  of  a  concentrated  solution  of  sodium  hydrogen 
sulphate  and  add  concentrated  hydrochloric  acid  gradually. 

Examine  with  a  lens.  The  interaction  of  salt  with  sulphuric 
acid,  or  of  hydrochloric  acid  with  sodium  hydrogen  sulphate, 
is  partial.  It  stops  when  all  four  substances,  in  certain  fixed 
quantities,  are  present  in  each  c.c.  of  the  liquid.  In  Exercise  45, 
the  escape  of  the  hydrochloric  acid  removes  it  from  the  sphere 
of  the  change  and  causes  the  reaction  to  proceed  to  completion 
in  one  direction.  In  this  exercise  the  insolubility  of  salt  in 
hydrochloric  acid  takes  the  salt  out  of  the  conflict  and  pushes 
the  reaction  to  completion  in  the  other  direction. 

EXERCISE  48 

THE  ACTION  OF  HYDROCHLORIC  ACID  UPON 
METALS 

Apparatus.  —  Beaker.  Eight  small  test  tubes.  Medicine  dropper. 
Watch  glass. 

Materials.  —  («)  Sodium.  (b)  Zinc  (granulated  and  dust).  Sheet 
copper.  Aluminium  turnings.  Test  lead.  Iron  filings.  Magnesium 
ribbon.  Mercury. 

Method.  —  See  textbook,  page  219,  section  301. 

(a)  Drop  a  2  mm.  (no  larger)  piece  of  sodium  into  5  c.c.  of 
concentrated  hydrochloric  acid  in  a  small  beaker.  Does  hydro- 
gen escape  ?  Hold  a  burning  match  close  to  the  globule. 
Why  is  the  flame  of  the  burning  gas  yellow  ? 

(6)  Dilute  20  c.c.  of  concentrated  hydrochloric  acid  with 
20  c.c.  of  water.  Place  in  separate  test  tubes  1  c,e.  of  granu- 


ACTION  OF  HYDROCHLORIC  ACID  UPON  METALS     65 

lated  zinc,  zinc  dust,  aluminium  turnings,  iron  filings,  and  test 
lead.  In  a  sixth  tube  place  1  sq.  cm.  of  sheet  copper,  in  a 
seventh,  3  cm.  of  magnesium  ribbon  coiled  into  a  spiral,  and  in 
an  eighth,  1  c.c.  of  mercury,  using  a  medicine  dropper.  Add  to 
each  tube  5  c.c.  of  the  mixture  of  hydrochloric  acid  and  water. 

Notice  and  record  any  change  in  each  tube.  If  no  change 
is  evident,  heat  gently,  but  remember  that  gas  escaping  while 
the  flame  is  used  may  be  steam  or  hydrogen  chloride.  If  the 
escape  of  gas  continues  while  the  flame  is  withdrawn,  there  is 
evidence  that  the  acid  and  the  metal  are  interacting.  Hydro- 
gen can  be  identified  by  burning  it,  but  remember  that,  when 
much  diluted  with  other  gases,  it  does  not  burn.  Does  the 
hydrogen  come  from  the  metal  or  the  acid  ?  Arrange  the 
metals  in  a  list,  beginning  with  the  most  active. 

When  interaction  occurs,  there  must  be  another  product. 
What  must  it  be  in  each  case  ? 

In  order  definitely  to  prove  the  formation  of  the  second 
product,  evaporate  one  of  the  solutions  to  dryness  in  a  watch 
glass  laid  upon  a  beaker  half  full  of  water,  which  is  gently 
boiled.  Wait  until  the  action  is  over,  and  filter,  if  necessary, 
before  evaporating. 

Did  you  notice  any  difference  in  the  behavior  of  zinc  dust 
and  granulated  zinc  ?  If  so,  what  is  the  cause  ? 


66          LABORATORY   STUDIES  IN   CHEMISTRY 

EXERCISE  49 

THE  ACTION   OF  HYDROCHLORIC  ACID  UPON 
OXIDES 

Apparatus.  —  Two  watch  glasses  8.5  cm.  in  diameter.  Five  small 
test  tubes.  Beaker.  Funnel. 

Materials.  —  Magnesium  oxide.  Zinc  oxide.  Mercuric  oxide. 
Cupric  oxide.  Lead  oxide.  Filters. 

Method.  —  See  textbook,  page  221. 

Place  1  c.c.  of  magnesium  oxide  in  a  small  test  tube.  Do 
the  same  with  the  other  oxides,  using  a  separate  tube  for  each. 
Add  to  each  tube  2  c.c.  of  water  and  2  c.c.  of  cone,  hydro- 
chloric acid.  Warm  gently,  but  not  to  boiling.  Is  gas 
evolved  ?  Be  careful  to  distinguish  between  mere  boiling  and 
the  escape  of  gas.  The  former  ceases  when  the  burner  is 
removed  —  the  latter  continues.  What  becomes  of  the  hy- 
drogen of  the  acid  and  the  oxygen  of  the  oxide  ?  What,  then, 
must  be  the  two  products  in  each  case  ? 

Complete  the  following  equations,  supplying  coefficients 
where  needed:  — 

MgO 
ZnO 


CuO  +  :rHCl->CuCl2  +, 
PbO  +  *HCl->PbCl2  +. 

Prove  by  evaporating  some  of  the  filtered  liquids,  as  in  the 
preceding  exercise,  that  these  chemical  changes  occur.  Use  a 
new  filter  for  each  substance  and  wash  the  funnel  each  time 
before  using  it  again.  If  time  presses,  the  five  evaporations 
can  be  distributed  to  different  students. 

Contrast  the  behavior  of  hydrochloric  acid  with  mercury  and 
with  mercuric  oxide  (Exercise  48). 

Contrast  the  behavior  of  hydrochloric  acid  with  lead  and 
with  lead  oxide. 


FLAME   TESTS  67 

Contrast  the  behavior  of  hydrochloric  acid  with  copper  and 
with  copper  oxide. 

Contrast  the  behavior  of  hydrochloric  acid  with  zinc  and 
with  zinc  oxide.  Explain. 

EXERCISE  50 
FLAME   TESTS 

Apparatus.  —  Wire  cutter.     Cobalt  glass.     Two  small  test  tubes. 

Materials.  —  Nitrates  of  calcium,  barium,  strontium,  sodium,  and 
potassium.  The  chlorides  can  be  used  instead.  Solution  of  lithium 
chloride.  Iron  wire  No.  20. 

Method.  —  See  textbook,  pages  209,  241,  262,  312. 

Obtain,  on  five  small  pieces  of  paper,  0.5  c.c.  (not  more)  of 
each  of  the  nitrates  mentioned.  Take  in  a  clean  test  tube  1  c.c. 
(not  more)  of  lithium  chloride  solution.  Make  a  2  mm.  loop 
on  the  end  of  a  15  cm.  (6  in.)  piece  of  iron  wire.  Dip  the  loop 
and  the  adjacent  part  of  the  wire  into  a  test  tube  (not  the  bottle) 
containing  5  c.c.  of  concentrated  hydrochloric  acid,  and  hold  it 
in  the  blue  flame  of  the  burner  until  it  gives  no  color  to  the 
flame.  Clean  the  wire  in  this  way  after  each  test,  before  using 
it  again.  If  you  find  it  impossible  to  get  the  wire  so  clean  that 
it  gives  no  color  to  the  flame,  discard  it  and  get  a  fresh  piece. 
Discard  the  acid  at  the  end  of  the  work. 

Take  up  a  trace  of  calcium  nitrate  on  the  loop,  hold  it  in  the 
lower,  outer  part  of  the  flame,  observe  and  record  the  color. 
Do  the  same  with  each  of  the  others.  The  wire  may  be  mois- 
tened when  dipped  into  the  salt.  Or,  if  the  wire  is  red  hot, 
enough  of  the  salt  will  usually  adhere  to  it  to  give  the  result. 

Look  at  the  potassium  flame  and  also  at  the  sodium  flame 
through  cobalt  glass.  Which  kind  of  light  is  quenched  by  the 
glass  and  which  transmitted  ?  Does  this  suggest  a  method  of 
detecting  potassium  in  the  presence  of  sodium?  Mix  the 
nitrates  of  the  two  metals  and  look  at  the  flame  color  of  the 
mixture  without  the  glass.  Which  metal  do  you  detect  ?  Now 
use  the  glass.  Eesult  ?  If  a  spectroscope  is  at  hand,  use  it  to 
examine  the  spectrum  of  sodium. 


68          LABORATORY   STUDIES   IN   CHEMISTRY 

EXERCISE   611 

PREPARATION   OF    SODIUM   HYDROGEN   CARBON- 
ATE  AND   SODIUM   CARBONATE 

(Solvay  Process) 

Apparatus.  —  Gas-generating  bottle  with  two-hole  rubber  stopper 
bearing  thistle  tube  and  delivery  tube,  bent  twice  at  right  angles. 
Test  tube  with  one-hole  rubber  stopper  and  delivery  tube.  Iron  dish 
(porcelain  will  answer,  with  care).  Graduated  cylinder.  Trip  scales. 
Large  test  tube  with  cork.  Large  test  tube. 

Materials.  —  Table  salt.  Ammonium  carbonate.  Marble  chips. 
Sodium  hydrogen  carbonate.  Filters.  Manila  paper.  Limewater. 

Method.  —  See  textbook,  page  323. 

(a)  Place  25  c.c.  strong  ammonia  and  15  c.c.  water  in  the 
large  test  tube  and  add  8  grams  of  ammonium  carbonate  (pow- 
dered). Cork  and  shake  until  the  latter  is  dissolved.  Add  an 
excess  of  sodium  chloride  and  shake  persistently  until  the 
liquid  is  saturated. 

Decant  the  clear  liquid  into  a  test  tube  and  pass  in  carbon  di- 
oxide in  a  slow  stream  for  half  an  hour,  or  until  an  abundant 
precipitate  of  sodium  hydrogen  carbonate  separates.  Mean- 
while go  on  with  (b)  or  (c).  The  carbon  dioxide  is  made  from 
marble  and  hydrochloric  acid  (Exercise  21).  Cover  the  marble 
with  water  and  add  concentrated  hydrochloric  acid  until  you 
obtain  a  steady  evolution  of  gas.  When  the  current  of  gas 
slackens,  add  fresh  acid.  Filter  the  sodium  hydrogen  carbon- 
ate and  dry  it  between  folds  of  manila  paper.  Note  its  appear- 
ance and  taste. 

(6)  Transformation  of  sodium  hydrogen  carbonate  into  so- 
dium carbonate. 

1  In  order  to  finish  in  time,  it  is  necessary  to  assign  (a),  (&),  and  (c) 
to  different  groups  of  students.  Or  (a)  may  be  carried  out  one  week  and 
(&)  and  (c)  the  next,  the  sodium  hydrogen  carbonate  being  dried  in  the 
meanwhile.  The  time  required  to  saturate  with  carbon  dioxide  can  be 
reduced  by  drawing  out  the  end  of  the  delivery  tube  so  as  to  produce 
small  bubbles. 


HYDROGEN  FLUORIDE  69 

Place  2  c.c.  sodium  hydrogen  carbonate  in  a  test  tube  and 
support  in  a  horizontal  position.  The  delivery  tube  dips  into 
limewater.  Heat  gently,  not  hot  enough  to  color  the  flame 
yellow.  What  gas  escapes  ?  What  condenses  in  the  cool  part 
of  the  tube  ?  Complete  the  equation:  — 


+  ...  4-  - 

Compare  the  taste  of  the  product  with  that  of  sodium  hydro- 
gen carbonate. 

(c)  Weigh  10  grams  of  sodium  hydrogen  carbonate  in  a 
weighed  iron  or  porcelain  dish.  Heat  at  first  gently,  then  in- 
tensely. Let  cool  and  reweigh.  Compare  the  taste  of  the 
product  with  that  of  sodium  hydrogen  carbonate.  What  is  the 
loss  in  weight  ?  Complete  the  equation  in  (6).  Calculate 
from  the  completed  equation  the  amount  which  10  grams  should 
lose.  What  is  the  error  of  your  determination  ? 

EXERCISE  52 
HYDROGEN  FLUORIDE 

Apparatus.  —  Lead  dish.     Forceps.     Glass  rod.     Agate  pan. 
Materials.  —  Powdered  fluorspar    (calcium  fluoride,  CaF2).      Red 
and  blue  litmus  paper.     Paraffin.     Glass  plate.     Pins. 
Methed.  —  See  textbook,  page  263. 

Place  2  c.c.  of  powdered  fluorspar  in  the  lead  dish,  moisten 
but  do  not  cover  it  with  concentrated  sulphuric  acid,  support  the 
dish  5  cm.  (2  in.)  above  a  small  flame;  and  .allow  it  to  get  warm. 
Wet  a  glass  rod  with  ammonia  and  hold  it  over  the  dish.  Do 
not  let  any  ammonia  fall  into  the  dish.  Remembering  the 
behavior  of  ammonia  with  hydrogen  chloride  (see  textbook, 
page  236),  explain  its  behavior  with  the  hydrogen  fluoride,  HF. 
Write  the  equation  for  the  combination  of  ammonia  and 
hydrogen  fluoride  and  name  the  product.  Hold  over  the  dish  a 
piece  of  red  and  a  piece  of  blue  litmus  paper.  Both  should  be 
damp. 


70          LABORATORY   STUDIES   IN   CHEMISTRY 

Complete  the  equation  :  — 


What  is  the  advantage  of  using  an  acid  like  sulphuric, 
which  does  not  vaporize  easily,  in  this  experiment  ?  Why 
would  it  be  impossible  to  use  hydrochloric  or  nitric  acid, 
although  both  are  more  active  than  sulphuric  ?  Compare 
textbook,  page  297. 

Support  a  glass  plate  10  cm.  (4  in.)  above  a  small  flame.  Rub 
the  upper  side  of  the  warm  plate  with  a  piece  of  paraffin  until 
you  have  covered  it  evenly.  Let  cool.  Write  the  name  of  the 
element  which  is  combined  with  hydrogen  in  hydrogen  fluoride 
upon  the  plate  with  a  pin,  being  careful  to  expose  the  glass. 
Write  also  the  year  of  the  isolation  of  fluorine  and  the  name 
of  the  great  French  chemist  who  first  isolated  it.  (See  text- 
book, page  264.)  Cover  the  dish  with  the  plate,  paraffin  side 
down,  in  such  a  way  that  your  writing  is  completely  exposed  to 
the  gas  in  the  dish.  Let  stand  for  half  an  hour  or  more.  The 
warmer  the  place,  the  better.  Do  not  heat  with  the  flame. 
Drop  the  plate  into  a  pan  of  boiling  water  to  remove  the 
paraffin.  Take  it  out  with  forceps,  wipe,  and  examine. 


BROMINE  71 

EXERCISE  53 
BROMINE 

Apparatus.  —  Large  test  tube.     Four  small  test  tubes.     Glass  rod. 

Materials.  —  Potassium  bromide  (powder).  Manganese  dioxide 
(powder).  Potassium  iodide  solution.  Chloroform.  Ether.  Car- 
bon disulphide.  Bromine.  Red  and  blue  litmus  paper.  Potassium 
iodide  starch  paper.1 

Method.  —  See  textbook,  pages  260, 261, 262.     Note  the  equation  :  — 

2  NaBr  +  Mn02  +  3H2SO4  ->-  MnSO4  +  2  NaHSO4  +  Br2. 

(a)  Place  1  c.c.  water  in  a  small  test  tube.  Add  2  c.c.  con- 
centrated sulphuric  acid.  Cool.  Mix  1  c.c.  potassium  bromide 
powder  with  2  c.c.  manganese  dioxide  powder  on  paper  and 
place  in  another  test  tube.  Add  enough  of  the  diluted  sul- 
phuric acid  to  moisten  the  mass.  Warm  gently.  Bromine 
vapor  escapes.  Note  color  and  odor.  (Care!)  Hold  in  the 
vapor  a  drop  of  potassium  iodide  solution  (glass  rod).  If  the 
color  in  the  drop  is  due  to  liberated  iodine,  what  else  must  be 
formed  at  the  same  time  ? 

Hold  a  piece  of  potassium  iodide-starch  paper  in  the  vapor. 
Potassium  iodide  does  not  color  starch,  as  the  whiteness  of 
the  unused  paper  proves.  Iodine,  on  the  other  hand,  colors 
starch  deep  blue  (delicate  test  both  for  iodine  and  starch). 
Explain,  then,  the  behavior  of  the  paper  in  bromine  vapor. 

Remove  the  flame  and  stop  the  production  of  bromine  by 
filling  the  tube  with  water.  Other  soluble  bromides  would 
behave  like  potassium  bromide  in  this. experiment,  and  other 
soluble  iodides  like  potassium  iodide.  The  potassium  salts 
are  used  merely  because  they  are  most  easily  obtained. 

CAUTION:  Ether  and  carbon  disulphide  must  not  be  used  in  the 
vicinity  of  flame.  Bottles  containing  them  must  be  kept  stoppered. 

1  To  make  this,  boil  1  c.c.  starch  powder  with  100  c.c.  water,  add  a 
1  mm.  crystal  of  potassium  iodide,  dip  strips  of  filter  paper  1  cm.  wide 
in  the  liquid,  and  hang  them  over  a  piece  of  glass  tubing  to  dry. 


72          LABORATORY   STUDIES   IN   CHEMISTRY 

(6)  Add  one  drop  of  bromine  to  15  c.c.  of  water  in  a  small 
test  tube.  Shake  the  liquid  in  the  test  tube.  The  solution 
you  have  made  is  called  bromine  water.  Place  5  c.c.  of  it  in 
each  of  the  three  small  test  tubes. 

CAUTION:  Do  not  withdraw  the  stopper  of  the  bromine  bottle  alto- 
gether. Loosen  it  and  let  the  liquid  drip  out  between  stopper  and  bottle. 
Use  the  opportunity  to  notice  the  high  density  of  bromine.  Avoid  inhaling 
bromine  vapor. 

To  one  tube,  add  2  c.c.  of  ether,  cover  with  the  thumb  and 
shake.  The  color  serves  as  a  measure  of  the  concentration  of 
the  bromine  in  the  two  layers.  What  happens  to  the  bromine  ? 
Note  that  the  bromine  does  not  pass  completely  from  the  water 
to  the  ether  layer.  Whether  there  is  much  or  little  bromine 
present,  it  is  divided  between  the  water  and  the  ether  so  that 
the  value  of  the  fraction  — 

bromine  in  1  c.c.  water  layer 
bromine  in  1  c.c.  ether  layer 

is  always  the  same  and  very  much  less  than  unity. 

If  you  had  to  extract  the  bromine  as  completely  as  possible 
from  a  liter  of  bromine  water,  and  could  use  only  500  c.c.  of 
ether,  how  would  you  go  about  it  ?  Would  it  be  best  to  use 
the  ether  all  at  once  ?  Or  could  you  get  a  better  result  by 
shaking  up  with  a  small  portion  of  ether  first,  separating  the 
ether  solution  of  bromine,  shaking  up  the  water  again  with 
another  small  portion  of  ether,  and  so  on  ?  Why  ?  (Compare 
textbook,  page  31,  section  40.) 

Try,  in  the  second  tube,  2  c.c.  of  chloroform,  and  in  the  third, 
2  c.c.  of  carbon  disulphide.  Cover  and  shake  as  before.  In 
these  cases,  also,  the  water  competes  with  the  other  liquid  for 
the  bromine. 

(c)  Hydrogen  bromide.  —  Place  1  c.c.  of  potassium  bromide 
crystals  in  a  test  tube  and  cover  with  a  mixture  of  3  volumes 
of  sulphuric  acid  and  1  volume  of  water.  Use  a  gentle  heat. 
Try  the  action  of  the  gas  upon  red  and  blue  litmus  paper. 


IODINE  73 

Hold  a  drop  of  ammonia  in  the  gas.     Make  a  comparison  be- 
tween hydrogen  bromide  and  hydrogen  chloride. 

Pure  hydrogen  bromide  is  colorless.  Had  the  gas  any  color 
in  this  experiment?  Eecalling  the  color  of  bromine  vapor, 
what  did  the  color  of  your  gas  in  this  experiment  indicate  ? 
Draw  a  conclusion  regarding  the  stability  of  hydrogen  bromide 
as  compared  with  hydrogen  chloride.  Hydrogen  iodide  (HI) 
cannot  be  prepared  at  all  by  the  action  of  sulphuric  acid  on 
iodides,  because  it  is,  for  the  most  part,  decomposed  with 
liberation  of  iodine.  (See  textbook,  page  259.)  How  about 
its  stability?  Inquire  of  the  instructor  about  the  stability 
of  the  hydrogen  compounds  of  this  series  and  read  up  the 
matter  in  the  textbook,  page  267. 


EXERCISE  64 
IODINE 

Apparatus.  —  Watch  glass  (large  enough  to  cover  evaporating 
dish).  Graduated  100  c.c.  cylinder.  Evaporating  dish.  Two  large 
test  tubes,  one  of  which  must  be  dry.  Four  small  test  tubes. 

Materials.  —  Potassium  iodide.  Iodine.  Manganese  dioxide 
(powder).  Starch  solution.  Alcohol.  Ether.  Carbon  disulphide. 
Chloroform.  Filter  paper. 

Method.  —  See  textbook,  pages  258, 259,  260.  Note  the  equation :  — 
2  KI  +  MnO2  +  3  H2SO4->MnSO4  +  2  KHSO4  +  I2. 

CA  UTION:   Do  not  allow  iodine  to  come  into  contact  with  the  skin. 

(a)  Place  1  c.c.  of  water  in  a  small  test  tube  and  add  2  c.c. 
concentrated  sulphuric  acid.  Cool.  Mix  1  c.c.  powdered 
potassium  iodide  with  2  c.c.  manganese  dioxide  powder  on 
paper.  Transfer  to  a  dry  dish.  Moisten  the  mixture  with 
three  to  four  drops  of  the  diluted  sulphuric  acid.  Cover  the 
dish  with  a  watch  glass  which  is  two  thirds  rilled  with  cold 
water  to  keep  it  cool.  Support  the  dish  10  cm.  (4  in.)  above  a 
2  cm.  (0.8  in.)  flame.  When  a  sufficient  sublimate  collects  on 


74          LABORATORY   STUDIES   IN   CHEMISTRY 

the  watch,  glass,  extinguish  the  flame.  Dip  a  strip  of  filter 
paper  into  starch  solution  and  hold  it  in  the  vapor  from  the 
dish.  Result  ?  Examine  the  sublimate  on  the  watch  glass. 

Iodine  stains  upon  the  hands  can  be  removed  by  rubbing 
with  a  wet  crystal  of  sodium  thiosulphate  (commonly  called 
hyposulphite  or  hypo). 

(6)  Gently  warm  a  large  test  tube  and  throw  in  a  crystal  of 
iodine.  Notice  color  and  odor  of  iodine  vapor.  Invert  the 
tube  and  notice  the  high  specific  gravity  of  iodine  vapor.  If 
the  formula  of  iodine  is  I2,  what  would  the  specific  gravity  of 
the  vapor  be,  referred  to  oxygen  ?  Referred  to  air  ? 

Use  the  same  test  tube  to  study  the  solubility  of  iodine  in 
alcohol.  Take  one  crystal  of  iodine  and  3  c.c.  alcohol.  Shake. 
This  alcoholic  solution  of  iodine  is  called  tincture  of  iodine  in 
pharmacy. 

CAUTION:  Ether  and  carbon  disulphide  must  not  be  used  near  a 
fiame. 

Fill  a  large  test  tube  one  half  with  water,  add  three  crystals  of 
iodine,  warm, — not  quite  to  boiling-point  —  and  shake.  Judge 
of  the  solubility  of  iodine  in  water  by  the  color  of  the  liquid. 
Place  10  c.c.  of  the  clear  solution  in  each  of  four  small  test 
tubes.  Use  three  of  these  to  ascertain  the  effect  of  shaking 
(1)  with  2  c.c.  ether,  (2)  with  2  c.c.  chloroform,  (3)  with  2  c.c. 
carbon  disulphide.  Discuss  the  results  from  the  same  point  of 
view  as  the  similar  experiments  with  bromine  (Exercise  53). 

To  the  fourth  tube,  add  10  c.c.  starch  solution.  Mix  thor- 
oughly. Reserving  the  remainder  of  the  blue  liquid,  pour 
1  c.c.  of  it  into  a  clean  graduated  cylinder.  The  cylinder  now 
contains  0.0001  gram  of  iodine.  Add  water  to  the  100  c.c.  mark 
and  mix  thoroughly  by  covering  the  cylinder  with  the  hand 
and  upsetting  it  several  times. 

Now  pour  off  half  the  liquid,  fill  again  to  100  c.c.,  and  mix. 
Place  the  cylinder  on  a  piece  of  white  paper  and  look  down 
through  it.  How  much  iodine  does  the  cylinder  now  contain  ? 
Proceed  in  this  way  until  it  becomes  impossible  to  perceive 
the  color. 


SILVER  COMPOUNDS  OF  THE   HALOGENS          75 

What  is  the  smallest  quantity  of  iodine  which  you  can  de- 
tect by  means  of  the  test  with  starch.  Is  the  test  delicate  ? 

Heat  the  remainder  of  the  original  mixture  of  iodine  and 
starch  solution  nearly  to  the  boiling  point  (80°).  Eesult? 
Cool  at  once  in  a  stream  of  water.  Eesult  ? 


EXERCISE   65 
SILVER  COMPOUNDS   OF  THE   HALOGENS 

(Tlie  Replacement  of  One  Halogen  by  Another) 
Apparatus.  —  Porcelain  dish.     Six  small  test  tubes. 
Materials.  —  Chlorine  water.     Bromine  water.    Potassium  bromide. 
Potassium   iodide.     Carbon  disulphide.     Potassium  chloride.     Silver 
nitrate  solution.     Salt.     Mossy  zinc.     Distilled  water. 
Method.  —  See  textbook,  pages  260  and  261. 

CA  UTION:     Do  not  allow  silver  nitrate  or  its  solution  to  come  into 
contact  with  the  skin. 

(a)  *  Dissolve  0.5  c.c.  sodium  chloride  in  5  c.c.  distilled  water 
and   add  3  c.c.   silver  nitrate  solution.        Shake  vigorously. 
Transfer  the  precipitate,  by  rinsing  with  water,  to  a  dish,  pour 
off  the  water,  add  a  0.5  cm.  bit  of  mossy  zinc  and  one  drop  of  con- 
centrated sulphuric  acid.      Cover  with  a  paper  to  exclude  the 
light  and  examine  from  time  to  time.     The  visible  product  is 
silver.     What  else  must  be  formed  ?     Notice  that  the  change 
spreads  through  the  mass  and  that  the  silver  chloride  is  all  con- 
verted into  silver,  although  most  of  it  never  touches  the  zinc  at 
all.     This  might  be  called  chemical  action  at  a  distance.     It  can 
be  readily  explained,  using  the  ideas  of  the  ionization  hypothesis, 
but  the  full  explanation  lies  beyond  the  scope  of  this  book. 
Remove  the  unused  zinc,  wash  the  silver  well  with  water,  and 
ask  the  instructor  what  to  do  with  it. 

(b)  Dissolve  a  1  mm.  crystal  of  potassium  chloride  in  5  c.c. 

1  (a)  and  (6)  should  be  started  at  the  beginning  of  a  laboratory  period 
and  allowed  to  stand  until  near  the  end. 


76          LABORATORY   STUDIES   IN   CHEMISTRY 

of  distilled  water  in  a  small  test  tube.  In  two  other  tubes, 
dissolve  1  inm.  crystals  of  potassium  bromide  and  potassium 
iodide  each  in  5  c.c.  distilled  water.  Add  to  each  tube  1  c.c. 
silver  nitrate  solution  and  shake.  Names  and  formulas  of  the 
precipitates  ?  Equations  ?  Use  half  of  each  precipitate  to 
study  the  solubility  in  ammonia.  Result  ?  Stand  the  other 
half  in  bright  sunlight  or  the  brightest  light  available  as  long 
as  possible.  Result  ? 

CA  UTION  :  Carbon  disulphide  must  not  be  used  near  aflame. 

(c)  Dissolve  a  1  mm.  crystal  of  potassium  bromide  in  5  c.c. 
water  in  a  small  test  tube.  Add  2  c.c.  carbon  disulphide  and 
shake.  Does  chemically  combined  bromine  behave  like  free 
bromine  toward  carbon  disulphide  ?  To  discuss  the  result  ac- 
curately, we  should  use  the  language  of  the  hypothesis  of  ion- 
ization.  The  water  solution  of  potassium  bromide  contains 
bromine  ions  (Br).  These  are  colorless.  Also  they  are  held 
tenaciously  by  the  water  and  scarcely  enter  the  carbon  disul- 
phide at  all. 

Now  add  3  c.c.  chlorine  water  and  shake.  Result?  The 
result  can  be  summed  up  in  the  statement  that  the  chlorine 
combines  with  the  potassium,  setting  free  the  bromine,  which 
dissolves  in  the  carbon  disulphide.  Speaking  in  terms  of  the 
ionization-idea,  the  chlorine  (C12)  takes  the  negative  charges 
from  two  bromine  ions,  producing  two  chlorine  ions  (Cl)  and 
bromine  (Br2),  which  dissolves  in  the  carbon  disulphide. 


The  result  may  be  said  to  prove  that  the  "  affinity  "  of  chlo- 
rine for  potassium  is  greater  than  that  of  bromine.  It  would 
be  more  exact  to  say  that  it  shows  that  the  tendency  of  chlo- 
rine to  exist  as  an  ion  is  greater  than  that  of  chlorine. 

(d)  Repeat  (c),  using  a  1  mm.  crystal  of  potassium  iodide, 
instead  of  the  potassium  bromide.     Which  has  the  "  strongest 
affinity  "  for  potassium,  chlorine  or   iodine  ?     More  exactly, 
which  has  the  strongest  tendency  to  exist  as  ion  ? 

(e)  Repeat  (c),  using  a  1  mm.  crystal  of  potassium  iodide 


NEUTRALIZATION   (1)  77 

with  the  water  and  carbon  disulphide  as  before,  but,  instead  of 
the  3  c.c.  chlorine  water,  add  0.5  c.c.  bromine  water  and  shake. 
Which  has  the  "  strongest  affinity  "  for  potassium,  bromine  or 
iodine  ?  Which  has  the  strongest  tendency  to  exist  as  ion  ? 

EXERCISE  56 
NEUTRALIZATION  (1) 

Apparatus.  —  Beaker.    Porcelain  dish.     Lens.    Glass  rod. 
Materials.  —  Sodium  hydroxide.     Potassium  hydroxide.    Red  and 
blue  litmus  paper. 

Method.  —  See  textbook,  pages  245  and  246. 

CA  UTION :  Do  not  allow  potassium  hydroxide  or  sodium  hydroxide 
to  come  into  contact  with  the  skin. 

(a)  Let  concentrated  hydrochloric  acid  fall,  drop  by  drop 
(Care  /),  upon  a  2  cm.  (0.8  in.)  piece  of  sodium  hydroxide  in  a 
beaker.  It  is  best  to  withdraw  the  stopper  partially  and  allow 
the  acid  to  leak  out  between  the  stopper  and  the  bottle.  From 
time  to  time  put  a  small  drop  of  the  liquid  upon  red  and  a  drop 
upon  blue  litmus  paper,  using  a  thin  glass  rod.  Use  the  same 
paper  for  many  tests. 

When  the  stick  is  disintegrated  and  the  change  seems  com- 
plete (acid  reaction  to  litmus), -scrape  the  solid  product  into  a 
dish  and  dry  it  with  a  small  flame  kept  in  motion.  When 
entirely  dry  and  odorless,  let  cool  and  taste.  Note  shape  of 
the  crystals  with  a  lens  or  microscope.  What  is  the  solid? 
What  must  have  been  the  second  product  ?  Write  the  equa- 
tion. 

(6)  Let  concentrated  nitric  acid  fall,  drop  by  drop,  upon  a 
2  cm.  piece  of  potassium  hydroxide  (Care  !)  until  the  change  is 
complete  (litmus  paper).  Dissolve  the  result  in  the  smallest 
possible  quantity  of  hot  water  and  let  cool.  Shape  and  appear- 
ance of  the  crystals  ?  Equation  ? 


78          LABORATORY   STUDIES   IN   CHEMISTRY 

EXERCISE  67 

NEUTRALIZATION   (2) 

(Quantitative) 

Apparatus.  —  Burette.  Graduated  cylinder.  Balance  or  trip  scales. 
Beaker.  Porcelain  dish.  Thin  glass  rod. 

Materials.  —  Normal  acid.1  Sodium  hydroxide.  Potassium  hy- 
droxide. Litmus  solution.  Cochineal  solution. 

Optional.  —  Washing  soda.  Commercial  potassium  carbonate. 
Limewater. 

Method.  —  See  textbook,  page  256. 

Read  up  the  subject  of  neutralization  and  normal  acids  in  the 
textbook,  page  256.  One  cubic  centimeter  of  a  normal  acid 
neutralizes  the  molecular  weight  in  milligrams  of  sodium  hy- 
droxide or  potassium  hydroxide,  but  only  one  half  the  molecular 
weight  of  sodium  carbonate  or  potassium  carbonate. 

Clamp  the  burette  in  a  vertical  position.  Note  that  it  reads 
downward.  Thus,  when  halfway  between  9  and  10,  the  reading 
is  9.5  c.c.,  not  10.5.  If  the  burette  is  wet,  rinse  it  out  with  a  few 
drops  of  the  normal  acid  and  discard  the  latter.  Dry  beakers 
must  be  used  in  handling  the  normal  acid,  to  avoid  diluting  it. 

(a)  Dry  a  dish,  weigh  it,  and  weigh  in  it  4  grams  of  sodium 
hydroxide.  Add  50  c.c.  water  and  dissolve  the  sodium  hydroxide 
by  stirring,  using  a  gentle  heat  if  necessary.  Transfer  to  a 
graduated  cylinder  and  rinse  the  dish  into  the  cylinder  three 
times  with  small  quantities  of  water.  Dilute  to  100  c.c.  Mix 
thoroughly. 

1  Most  quickly  made  by  dissolving  63  grams  oxalic  acid  (C2H2O4,  2  H20) 
to  a  liter.  Trip  scales  are  accurate  enough  for  the  weighing.  It  is  well 
to  have  at  least  75  c.c.  for  each  student ;  more,  if  the  work  is  extended  to 
cover  sodium  carbonate,  pearlash,  etc.  The  student  can  readily  make  it 
himself  in  the  graduated  cylinder,  but  the  exercise  then  becomes  too  long 
for  the  usual  laboratory  period.  Use  cochineal  as  indicator  in  presence 
of  carbonic  acid.  Digest  a  1  cm.  layer  of  the  crushed  insects  under  half 
a  liter  of  alcohol  with  occasional  shaking.  Other  indicators  may  be  sub- 
stituted. Mohr  burettes  are  best  suited  to  elementary  work. 


NEUTRALIZATION   (2)  79 

Pour  exactly  20  c.c.  of  the  solution  of  sodium  hydroxide  into 
a  clean  beaker,  and  add  enough  litmus  solution  to  give  a  dis- 
tinct but  not  a  strong  color  (about  five  drops).  Fill  the  burette 
to  zero  with  the  normal  acid,  making  sure  that  the  portion 
below  the  pinchcock  is  also  filled.  Stand  the  beaker  on  a  piece 
of  white  paper  (filter  paper)  and  run  in  the  normal  acid  — 
10  c.c.  can  be  added  rapidly ;  then  add  one  drop  at  a  time,  stir- 
ring constantly,  until  the  color  change  occurs.  Calculate  the 
percentage  of  sodium  hydroxide  in  the  sample.  Remember 
that  20  c.c.  contains  ^  of  the  quantity  weighed  out.  Thus, 
suppose  that  19  c.c.  of  the  normal  acid  were  required.  Since 
each  cubic  centimeter  of  the  normal  acid  consumes  40  milli- 
grams of  sodium  hydroxide,  the  quantity  of  the  latter  present 
must  have  been,  in  grams,  0.040  x  19  =  0.76  gram  NaOH. 
The  20  c.c.  of  sodium  hydroxide  solution  used  contained 
4  X  ^  =  0.8  gram  commercial  NaOH.  So  the  percentage  of 
true  sodium  hydroxide  must  be :  — 

— =95  per  cent,  the  balance  being  impurities. 

0.8 

Repeat,  using  25  c.c.  of  the  sodium  hydroxide,  colored  with 
10  drops  of  cochineal  solution  instead  of  litmus.  Does  the 
volume  of  sodium  hydroxide  solution  taken  affect  the  result  ? 
Does  the  nature  of  the  indicator  affect  it  ?  Remember  that 
25  c.c.  contains  ^  of  the  quantity  of  sodium  hydroxide  you 
weighed  out. 

If  the  sodium  hydroxide  had  been  perfectly  pure,  what 
special  concentration  would  have  been  obtained  by  using  4 
grams  of  it  in  100  c.c.  ?  To  what  extent  did  your  solution 
depart  from  this  concentration? 

(6)  Weigh  in  a  dish  5.6  grams  potassium  hydroxide  and 
repeat  the  whole  experiment,  making  the  same  calculations 
and  answering  the  same  questions. 

In  (c)  and  (d)  use  cochineal  and  omit  the  experiment  with 
litmus. 

(c)  Make  the  same  experiment  with  14.3  grams  of  washing 


80          LABORATORY   STUDIES   IN   CHEMISTRY 

soda  crystals.  Calculate  the  percentage  of  sodium  carbonate, 
Na2C03.  How  close  is  your  result  to  that  calculated  from  the 
formula  Na^CQilOBW)? 

(d)  Make  the  same  experiment  with  6.9  grams  commercial 
potassium  carbonate  (pearlash).     Calculate  the  percentage  of 
potassium  carbonate,  K2C03. 

(e)  Measure  100  c.c.  of  limewater  into  a  beaker,  color  with 
litmus  or  cochineal,  and  add  normal  acid  from  the  burette  until 
the  change  in  color  takes  place.     Be  careful,  as  only  a  small 
volume  of  acid  will  be  needed.     Since  the  molecular  weight  of 
Ca(OH)2  is  74,  1  c.c.  of  normal  acid  equals  -^  or  37  milligrams 
of  slaked  lime.     Calculate  the  weight  of  calcium  hydroxide  in 
100  c.c.  of  limewater. 

According  to  the  most  exact  figures  obtainable,  100  c.c.  lime- 
water  at  room  temperature  (20°  C.)  contains  0.165  gram  calcium 
hydroxide.  What  was  the  error  of  your  result  ?  The  white 
precipitate  formed  is  calcium  oxalate :  — 

Ca(OH)2  +  H2C204->CaC204  +  2  H2O. 

EXERCISE  68 
THE  ACTION   OF  BASES   ON   SALTS 

Apparatus.  —  Beaker.     Small  test  tubes.     Mortar  and  pestle. 

Materials.  —  Sodium  hydroxide.  Copper  sulphate.  Silver  nitrate. 
Mercuric  chloride.  Zinc  sulphate.  Lead  nitrate.  Aluminium  sul- 
phate. Ferrous  sulphate.  Mercuric  oxide. 

Method.  —  The  hydroxides  of  the  heavy  metals  (see  textbook, 
page  368)  are  mostly  insoluble  in  water.  They  precipitate  when 
sodium  hydroxide  solution  is  added  to  a  solution  containing  a  salt  of 
the  corresponding  metal.  Some  insoluble  hydroxides  dissolve  in  ex- 
cess of  sodium  hydroxide  solution. 

(a)  Dissolve  10  grams  of  sodium  hydroxide  in  80  c.c.  water 
in  a  beaker.  Aid  the  solution  by  a  small  flame  and  gentle 
stirring.  Cool  the  liquid.  Dissolve  0.5  c.c.  copper  sulphate 
in  5  c.c.  water  in  a  small  test  tube.  Cool,  if  you  have  used 


THE  ACTION  OP  BASES  ON  SALTS  81 

heat.     Add  5  c.c.  of  the  sodium  hydroxide  solution.     Complete 
the  equation  :  — 


Heat  the  contents  of  the  tube  to  gentle  boiling.     Kesult  ? 

Repeat,  using  a  1  mm.  crystal  of  silver  nitrate  instead  of  the 
copper  sulphate.  Boiling  is  necessary  only  in  the  case  of  cop- 
per sulphate.  Handle  silver  nitrate  with  paper,  not  with  the 
fingers.  Complete  the  equation  :  — 


x  AgNO3  +  y  NaOH->Ag2O 

Repeat,  using  0.5  c.c.  of  mercuric  chloride.  Complete  the 
equation  :  — 

HgCl2  -f  x  NaOH  ->  HgO  +  y  NaCl  +  .  ..  . 

Compare  this  mercuric  oxide  with  that  in  the  stock  bottle. 
Chemists  are  not  yet  agreed  upon  the  cause  of  the  striking 
difference. 

(b)  Dissolve  0.5  c.c.  zinc  sulphate  in  5  c.c.  water.  Add 
sodium  hydroxide  solution,  a  few  drops  at  a  time,  shaking  well 
after  each  addition.  When  a  considerable  precipitate  is  ob- 
tained, stop  to  examine  it  and  then  continue  the  addition  of 
sodium  hydroxide  until  you  have  added  10  c.c.  Complete  the 
equation  :  — 


What  happens  when  more  sodium  hydroxide  is  added  to  the 
precipitate  ? 

Treat  lead  nitrate  in  the  same  way  as  zinc  sulphate.  Com- 
plete the  equation  :  — 

Pb(NO3)2  +  zNaOH  ->  Pb(OH)2  +  .... 

Treat  aluminium  sulphate  in  the  same  way  as  zinc  sulphate. 
Complete  the  equation  :  — 

A12(S04)3  +  zNaOH  ->  2  A1(OH)3  +  .... 

What  important  difference  exists  between  the  substances  in 
(a)  and  those  in 


82          LABORATORY   STUDIES   IN   CHEMISTRY 

(c)  Select  a  clear  crystal  of  ferrous  sulphate  about  0.5  cm. 
in  diameter  and  hold  it  in  a  stream  of  water  until  the  surface 
is  dissolved  away.  Dry  with  paper  and  crush  in  a  clean 
mortar.  Powder  finely. 

Boil  10  c.c.  water  in  a  small  test  tube  to  expel  the  dissolved 
air  and  cool  in  a  stream  of  water.  Add  the  ferrous  sulphate 
and  dissolve  it  by  stirring.  Do  not  heat.  When  completely 
dissolved,  add  10  c.c.  sodium  hydroxide  solution.  The  precip- 
itate is  ferrous  hydroxide.  Complete  the  equation  :  — 

FeSO4  +  arNaOH  ->  Fe(OH)2  +  .... 

Shake  the  tube  vigorously  for  five  minutes  and  note  any 
change  in  the  precipitate.  It  passes  into  ferric  hydroxide. 
The  complete  equation  is :  — 

2  Fe(OH)2  +  O  +  H2O  ->  2  Fe(OH)3. 

EXERCISE  59 

THE  ACTION  OF  A  METAL  ON  A  SOLUTION  OF  A 
SALT   OF   ANOTHER   METAL 

Apparatus.  —  Scissors.  Tinner's  shears.  Lens.  Ten  small  test 
tubes. 

Materials.  —  (a)  Sheet  copper.  Sheet  zinc.  Copper  wire  No.  30. 
(b)  Silver  nitrate.  Mercuric  chloride.  Copper  sulphate.  Lead  nitrate. 
Tin  chloride  (stannous).  Zinc  sulphate.  Sandpaper.  Dennison 
labels,  small. 

Method.  —  See  textbook,  page  293. 

(a)  Cut  a  piece  of  sheet  copper  5x5  cm.  (2x2  in.). 
Clean  it  with  sandpaper  and  cut  it  into  five  strips  each  5x1 
cm.  (2  x  0.4  in.).  Prepare,  in  the  same  way,  five  strips  of 
sheet  zinc.  0.5  cm.  from  the  end  of  each  of  the  ten  metal 
strips  fasten  one  end  of  a  copper  wire  20  cm.  (8  in.)  long. 
The  wire  may  be  cut  with  ordinary  scissors. 

(6)  20  c.c.  dilute  solution  of  the  salts  listed  in  (b)  is  required. 
Prepare  by  dissolving  1  c.c.  of  the  salt  in  20  c.c.  water. 


METALS  AND  SALTS  83 

Heat,  if  necessary,  but  cool  before  using.  Use  a  separate  test 
tube  for  each  salt.  Tin  chloride  will  not  dissolve  clear  in  water 
alone.  Add,  therefore,  to  its  solution  a  few  drops  of  hydro- 
chloric acid.  Use  only  0.5  c.c.  of  silver  nitrate  and  of  mer- 
curic chloride.  Do  not  touch  either  of  these  two  with  the  fingers. 
Label  each  tube  with  the  formula  of  the  substance  it  contains 
and  also  with  the  symbol  of  the  metal  ion  formed  when  the 
substance  dissolves  in  water.  Obtain  this  information  from 
the  textbook.  Put  on  the  label,  also,  the  color  of  the  solution. 

Place  10  c.c.  of  each  of  the  solutions,  omitting  the  copper 
sulphate,  in  separate  test  tubes,  and  suspend  in  each  a  piece 
of  sheet  copper  so  that  1  cm.  (0.4  in.)  of  the  metal  is  above  the 
surface. 

In  the  same  way,  suspend  a  strip  of  zinc  in  another  10  c.c. 
of  each  solution,  omitting  the  zinc  sulphate.  Let  stand. 
After  a  time,  withdraw  the  strips  and  examine  them  minutely 
with  a  lens.  Use  the  upper  portion,  which  should  not  have 
been  wet  with  the  liquid,  for  comparison.  Be  prepared  for 
the  fact  that  finely  divided  metals  reflect  light  differently  and 
present  a  very  different  appearance  from  the  same  metals  in 
compact  polished  condition. 

What  appears  to  have  happened  ?  Is  the  deposit  on  the 
copper  the  only  product  ?  If  not,  what  must  be  the  second 
product,  in  each  case?  Note  carefully  any  changes  in  the 
colors  of  the  solutions.  Do  these  changes  confirm  your  con- 
clusions ?  State  your  results  in  a  table  of  four  columns,  put- 
ting in  the  first,  the  metal  used,  in  the  second,  the  substance 
in  solution,  in  the  third,  the  deposit,  and  in  the  fourth,  the 
other  product.  Write  an  equation  for  each  change,  first  in 
the  ordinary  way.  Then  write  the  more  simple  equations 
which  describe  the  same  changes  in  the  light  of  the  ionic 
theory. 


84          LABORATORY   STUDIES   IN   CHEMISTRY 

EXERCISE  60 
IONIZED  AND   UN-IONIZED   SOLUTIONS 

Apparatus.  —  Small  test  tubes,  some  of  which  must  be  dry. 

Materials.  —  Cupric  chloride.  Cobalt  chloride.  Cupric  sulphate. 
Cobalt  sulphate.  Alcohol  (95  per  cent).  Solution  of  hydrogen  chlo- 
ride in  toluene.  Mossy  zinc.  Magnesium  ribbon.  Iron  (small  nail). 
Marble  fragments. 

Method.  —  See  textbook,  page  288. 

Exercise  unusual  care  to  avoid  waste  of  the  cobalt  salts.  They  are 
expensive.  The  solution  of  hydrogen  chloride  in  toluene  is  easily 
made  by  passing  the  gas  into  toluene  until  the  latter  is  saturated. 
It  should  be  kept  in  a  tightly  stoppered  bottle. 

(a)  Dissolve  02  c.c.  of  cupric  sulphate  in  2  c.c.  water.  Do 
the  same  with  0.2  c.c.  cobalt  sulphate  and  with  0.2  c.c.  cobalt 
chloride  in  different  tubes.  Note  the  colors  of  the  liquids. 
Other  cupric  and  cobalt  compounds  in  dilute  water  solution  show 
the  same  colors,  respectively.  What  conclusion  can  be  drawn 
from  this  fact  ?  The  solutions  of  cupric  compounds  (which  all 
have  the  same  color)  and  the  solutions  of  cobalt  salts  (which 
all  have  the  same  color)  are  good  conductors  of  the  electric  current. 
What  follows  from  this,  regarding  the  condition  of  the  salt  ? 
Does  it  confirm  your  conclusion  drawn  from  the  color  ? 

Dissolve  0.3  c.c.  cobalt  chloride  in  3  c.c.  alcohol.  Do  the 
same,  in  a  separate  tube,  with  cupric  chloride.  Study  the  colors 
of  the  liquids  and  compare  them  with  the  water  solutions  con- 
taining the  same  metals.  Does  the  color  of  cobalt  chloride  in 
alcohol  resemble  the  color  of  water  solutions  of  cobalt  salts  ? 
Has  the  alcohol  solution  of  cupric  chloride  the  same  color  as 
cupric  compounds  dissolved  in  water  ?  What  conclusion  do 
you  deduce  regarding  the  condition  of  the  salts  in  the  solutions  ? 

These  alcoholic  solutions  are  all  nonconductors  of  the  current. 
Does  this  confirm  your  conclusion  drawn  from  the  colors? 
Can  you  think  of  any  method,  based  upon  a  study  of  the 
boiling  points  of  water  and  alcohol  solutions,  by  which  your 
conclusions  might  be  tested  ? 


HYDROLYSIS  85 

Pour  half  of  the  alcoholic  solution  of  cupric  chloride  into 
3  c.c.  water  in  a  small  test  tube.  Result  ?  Do  the  same  with 
the  alcohol  solution  of  cupric  chloride  in  another  tube.  Re- 
sult ?  What  is  indicated  by  the  fact  that  the  color  changes  and 
the  appearance  of  conductivity  in  the  liquids  are  simultaneous  ? 

(6)  Obtain,  in  a  dry  test  tube,  5  c.c.  of  a  solution  of  hydro- 
gen chloride  in  toluene.  Test  the  behavior  of  this  liquid  in 
dry  tes"t  tubes  with  zinc,  magnesium,  iron  (small  nail),  and  a 
bit  of  marble  or  calcite.  Result  ?  Investigate  the  action  of 
ordinary  hydrochloric  acid  on  the  same  substances.  Result? 

The  water  solution  of  hydrogen  chloride  conducts  the 
electric  current,  but  the  toluene  solution  is  a  nonconductor. 
Explain  the  connection  between  chemical  activity  and  con- 
ductivity. 

EXERCISE  61 
HYDROLYSIS 

Apparatus.  —  Reading  glass  or  other  long  focus  lens.  Five  small 
test  tubes.  Glass  rod. 

Materials.  —  (a)  Cupric  chloride  (CuCl2).  Stannous  chloride 
(SnCl2).  Ferric  chloride  (FeCl8).  Cupric  sulphate  (CuSO4).  Alu- 
minium sulphate  (A12(SO4)3). 

Distilled  water.     Red  and  blue  litmus  paper. 

(6)  Sodium  carbonate  (Na2CO3).  Potassium  carbonate  (K2CO3). 
Sodium  sulphide  (Na2S). 

(c)  Sodium  chloride  (NaCl).  Potassium  chloride  (KC1).  Sodium 
nitrate  (NaNO3).  Potassium  nitrate  (KNO^). 

Method.  —  See  textbook,  page  289. 

Take  special  care  to  have  test  tubes  and  glass  rods  used  in  this  work 
perfectly  clean. 

NOTE  :  —  Before  doing  the  work,  read  up  the  subject  of  hydrolysis 
in  the  textbook.  In  testing  with  litmus  paper,  put  a  small  drop  of 
the  liquid  on  the  paper  with  a  glass  rod.  Use  the  same  paper  for 
many  tests.  In  the  interpretation  of  the  results,  remember  that  the 
reddening  of  blue  litmus  is  positive  proof  of  the  presence  of  an  acid 
7 


86          LABORATORY   STUDIES   IN   CHEMISTRY 

+ 
(that  is,  of  hydrogen  ions  H),  since  nothing  else  can  produce  the 

change  in  color.  The  turning  blue  of  red  litmus  is  proof  of  the  pres- 
ence of  a  base  (that  is,  of  hydro xyl  ions  OH) .  Absence  of  effect  on 
both  kinds  of  litmus  shows,  therefore,  that  neither  acids  nor  bases 

+ 
(H  and  OH  ions)  are  present  in  measurable  quantity. 

(a)  Dissolve  0.2  c.c.  of  each  of  the  substances  mentioned  in 
(a)  in  10  c.c.  distilled  water  in  a  small  test  tube.  Use 'a  sep- 
arate tube  for  each  substance.  Heat  until  solution  is  complete. 
Then  cool  in  a  stream  of  water. 

(1)  Are  the  liquids  completely  clear  ?      If  the  eye  alone 
does  not  detect  evidence  of  the  formation  of  a  precipitate,  a 
very  delicate  test  is  to  focus  a  beam  of  sunlight  in  the  liquid 
with  a  lens.     The  smallest  traces  of  solid  matter  make  the 
path  of  the  beam  visible,  on  the  same  principle  as  the  motes  in 
a  sunbeam.     Try  this  with  each  solution.     Try  it  also  with 
the  distilled  water  used,  for  comparison. 

(2)  Ascertain  the  action  of  each  liquid  upon  red  and  blue 
litmus  paper.     What  is,  in  each  case,  the  only  acid  which 
could  possibly  be  present?     What,  then,  must  be  the  other 
product?      Assuming  that  you  detected  evidence  of  the  for- 
mation of  precipitates  in  (1),  what  is  probably  the  nature  of 
the  precipitate  in  each  case  ?     Complete  the  following  equa- 
tions, supplying  coefficients  where  they  are  denoted  by  letters : 

CuCl2  +  *H20^±Cu(OH)2  +  ..., 

SnCl2  +  xH20^±Sn  (OH)2  +  •-, 

FeCls  4-  xH2O^±Fe(OH)3  +  -, 

CuSO4  -f  *H2O;±Cu(OH)2  +  ..., 

A12(SO4)8  +  x  H2O->?/  A1(OH)8  +  •••  • 

The  five  substances  in  (a)  are  salts  of  active  acids  and  in- 
active bases.  Explain  what  this  statement  means.  Do  your 
results  corroborate  it  ? 

(&)  Treat  the  substances  mentioned  in  (6)  in  the  same  way. 
Heating  and  the  examination  for  suspended  solid  matter  may 
be  omitted,  since  the  acids  and  bases  formed  by  hydrolysis  of 


SEPARATION  OF  LEAD,  SILVER,  AND  MERCURY    87 

these  three  salts  are  all  freely  soluble.  How  do  these  sub- 
stances differ  from  those  in  (a)  ?  What  is  the  only  base 
which  could  possibly  be  present  in  each  solution  ?  What, 
then,  must  be  the  second  product  in  each  case  ?  These  three 
substances  are  salts  of  inactive  acids  with  active  bases.  Ex- 
plain the  meaning  of  this  statement  and  its  bearing  upon  your 
results.  Complete  the  equations  :  — 


K2C03  +  x  H20  ^±  H2C03 


(c)  Investigate  the  four  substances  in  (c)  in  the  same  way. 
For  the  same  reasons  as  in  (6),  the  testing  for  separated  solid 
matter  can  be  neglected.  How  does  this  class  of  substances 
differ  from  the  other  two  ?  Is  there  reason  for  assuming  any 
interaction  between  the  salts  and  water?  These  four  sub- 
stances are  salts  of  active  acids  with  active  bases.  What  does 
this  mean  and  what  bearing  has  it  upon  your  results  ?  l 

EXERCISE  62  2 
SEPARATION  OF  LEAD,   SILVER,   AND  MERCURY 

Apparatus.  —  Small  test  tubes.  Beaker.  Funnel.  Glass  rod. 
Wire  gauze. 

Materials.  —  Solutions  of  lead  nitrate,  silver  nitrate,  and  mercu- 
rous  nitrate.  Potassium  chromate  solution  (1  :  20).  Filters.  Sheet 
copper.  Blue  litmus  paper. 

Method.  —  See  textbook,  page  233  (oable). 

(a)  (1)  To  5  c.c.  of  lead  nitrate  solution  in  a  small  test 
tube,  add  dilute  hydrochloric  acid  until  the  action  is  complete. 
Test  this  by  shaking  vigorously,  letting  the  precipitate  settle, 

1  If  the  time  allotted  to  the  subject  permits,  a  classroom  discussion  of 
these  phenomena  from  the  standpoint  of  the  ionization  hypothesis  would 
be  valuable. 

2  With  the  usual  laboratory  period  (ninety  minutes)  the  teacher  may 
find  it  best  to  take  up  (a),  (&),  and  (c)  one  week  and  (d)  and  (e)  the  next. 


88          LABORATORY   STUDIES   IN   CHEMISTRY 

and  adding  a  drop  or  two  of  hydrochloric  acid  to  the  liquid. 
Pour  off  the  liquid  as  completely  as  you  can  without  losing 
the  precipitate,  fill  the  tube  half  full  of  cold  water,  shake, 
and  again  pour  off.  What  is  removed  by  this  treatment  ? 

(2)  Dissolve  the  precipitate  in  the  smallest  possible  quantity 
of  hot  water.  At  once  divide  the  solution  into  three  equal 
portions.  Stand  the  first  aside  and  examine  it  when  cold. 
Result  ?  To  the  second,  add  2  c.c.  of  a  solution  of  potassium 
chromate.  Result  ?  To  the  third,  add  1  c.c.  of  sulphuric 
acid.  Result  ?  Complete  the  equations  :  — 


Pb(NO3)2  +  zHCl  ->  PbCl2  +  ..., 
PbCl2  +  K2Cr04  -+  PbCr04  +  -, 
PbCl2  +  H2S04  ->  PbS04  +  .... 

(6)  (1)  Treat  5  c.c.  silver  nitrate  solution  exactly  as  in 
(a)  (1). 

(2)  Test  the  solubility  of  silver  chloride  in  hot  water. 
Pour  off  the  water  and  divide  the  precipitate  into  two  portions. 
Stand  the  first  in  the  brightest  light  available  for  ten  minutes. 
Meanwhile,  test  the  action  of  ammonia  on  the  second  portion. 
Add  dilute  nitric  acid  to  the  ammonia  solution  until  the  odor 
of  ammonia  disappears.  Result?  Complete  the  equation  :  — 

AgNOs  +  HCl->  AgCl  +  -.. 

(c)  Treat  5  c.c.  of  mercurous  nitrate  solution  as  in  (a)  (1). 
Divide  the  precipitate  into  two  portions.     Does  hot  water  dis- 
solve mercurous  chloride  ?     What  effect  has  ammonia  upon  it  ? 

(d)  Mix  5  c.c.  each  of  the  solutions  of  lead,  silver,  and  mer- 
curous nitrates.     Add  dilute  hydrochloric  acid  until  it  forms 
no  further  precipitate.     Shake  well  and  filter.     Pour  a  little 
cold  water  over  the  precipitate.     Reject  the  filtrate.     What 
substances  are  contained  in  the  precipitate  ? 

(1)  Wash  the  precipitate  with  50  c.c.  boiling  water,  being  sure 
to  reach  every  part  of  it.  Preserve  the  liquid.  Which  of  the 
three  chlorides  does  it  contain  ?  Prove  by  using  the  test  with 
potassium  chromate  and  that  with  sulphuric  acid  as  in  (a)  (2). 


THE   BEAD  TESTS  89 

(2)  What  substances  are  still  on  the  filter  ?     Pour  ammonia 
over  it.     Which  dissolves  ?     Receive  the  liquid  in  a  clean  test 
tube  and  add  dilute  nitric  acid  to  it  until  the  ammonia  is  neu- 
tralized (litmus  paper). 

(3)  Which  chloride  has  caused  the  darkening  with  ammonia? 
Make  a  little  aqua  regia  by  pouring  1  c.c.  hydrochloric  acid  (con- 
centrated) into  0.5  c.c.  concentrated  nitric  acid.     Warm  it  and 
pour  it  over  the  filter,  receiving  the  filtrate  in  a  clean  test  tube. 
Dilute  with  10  c.c.  water  and  place  a  1  X  2  cm.  (0.4  X  0.8  in.) 
piece  of  clean  sheet  copper  in  the  liquid.     Let  stand.     Wash, 
rub  with  the  finger,  and  examine. 

(e)  Ask  for  an  unknown  solution  and  analyze  it  for  silver, 
mercury,  and  lead,  proceeding  systematically  as  in  (d).  Note 
that  the  metals  must  be  separated  from  each  other  before  the 
tests  can  be  applied.  In  writing  your  notes,  remember  that 
to  prove  the  absence  of  a  substance  is  frequently  just  as  im- 
portant (e.g.  in  cases  of  suspected  poisoning)  as  to  prove  its 
presence. 

EXERCISE   63 

THE   BEAD   TESTS1 

Apparatus.  —  Platinum  wire  (mounted  in  piece  of  glass  rod) .  Blow- 
pipe. Wing  top. 

Materials.  —  Borax  powder.  Microcosmic  salt  (sodium  ammonium 
phosphate). 

(a)  Cobalt  nitrate.  Nickel  nitrate.  Manganese  dioxide.  Chrome 
alum.  Copper  sulphate.  Ferric  chloride.  Sodium  carbonate. 

(6)  Orthoclase  (0.5  mm.  fragment). 

(c)   Optional.  —  Siderite,  rhodonite,  chrysocolla. 

Method.  —  See  textbook,  page  338. 

Either  the  Bunsen  burner  or  the  blowpipe  may  serve  as  the  source 
of  heat.  If  the  burner  is  used,  reduce  the  access  of  air  until  a  small 
yellow  area  appears  in  the  upper  portion  of  the  flame.  This  luminous 
area  contains  glowing  carbon.  It  is  called  the  reducing  flame.  The 

1  Many  teachers  will  prefer  to  inform  the  students  beforehand  what 
colors  will  be  obtained  in  the  beads  by  correct  work. 


90          LABORATORY   STUDIES   IN   CHEMISTRY 

strongest  oxidizing  flarne  is  the  extreme  upper  part  (blue),  but  any 
part  of  the  outer  mantle  can  be  used.  Clamp  the  burner  at  an 
angle  of  25°  with  the  vertical  to  avoid  dropping  substances  into  the 
chimney. 

If  the  blowpipe  is  employed,  wash  off  the  mouthpiece.  Use  the 
wing  top.  Re-read  the  directions  in  Exercise  6.  The  reducing 
flame  is  obtained  by  placing  the  tip  of  the  blowpipe  just  inside  of  the 
base  of  the  edge  of  the  flame  and  bending  down  the  flame  with  a 
gentle  blast.  It  should  be  somewhat  yellow  and  perfectly  steady  and 
noiseless.  It  should  surround  the  sample  completely.  In  all  blowpipe 
work  the  air-holes  at  the  base  of  the  burner  should  be  closed. 

It  is  convenient  to  assign  borax  and  microcosmic  salt  to  different 
groups  of  students. 

Bend  the  end  of  the  platinum  wire  into  a  circle  2  mm.  (0.08  in.) 
in  diameter.  Heat  the  loop  red  hot  and  dip  it  into  powdered 
borax.  Notice  the  swelling  up  due  to  loss  of  water  of  crystal- 
lization. Melt  the  anhydrous  borax  to  a  bead.  Touch  with 
the  hot  bead  a  speck  of  cobalt  nitrate  not  more  than  0.5  mm.  in 
diameter.  Return  to  the  flame.  When  the  bead  appears  clear, 
let  cool  and  examine.  If  the  bead  is  opaque,  too  much  cobalt 
nitrate  was  used.  Discard  it  and  make  another.  Much  more 
rarely  it  happens  that  the  color  is  pale  and  indistinct.  In 
that  case,  heat  again  and  take  up  an  additional  speck  of  cobalt 
nitrate.  Use  the  oxidizing  flame  in  melting  the  bead.  Then 
hold  it  persistently  in  the  reducing  flame  and  see  whether  the 
color  changes. 

Remove  the  bead  by  heating  it  red  hot  and  dipping  into 
water.  The  fragments  can  be  detached  from  the  wire  without 
difficulty.  Make  a  fresh  bead  and  remove  it,  to  cleanse  the 
wire  from  cobalt,  before  proceeding  to  the  next  test.  If  the 
third  bead  has  a  color,  discard  it  also.  A  clean,  colorless  bead 
should  be  used  for  each  test. 

In  the  same  way,  investigate  the  behavior  of  the  substances 
mentioned  in  (a),  each  time  studying  the  behavior  in  both 
flames.  The  result,  with  all  except  the  last,  is  due  to  the 
metal  of  the  salt.  Any  other  compounds  of  the  same  metals 
would  behave  in  the  same  way.  In  several  cases,  the  bead 


THE  BEAD   TESTS 


91 


while  hot  (not  red  hot)  has  a  different  color  from  that  which 
it  has  when  quite  cold.  Does  sodium  carbonate  give  any  color 
to  the  bead  ?  Notice  the  escape  of  carbon  dioxide  in  this  case. 
This  is  the  blowpipe  test  for  a  carbonate. 

Record  your  results  in  a  table  thus :  — 


NAME  OF 
COMPOUND 

FOEMULA 

COLOR  OF  BEAD 
O.F.1 

COLOR  OF  BEAD 
R.F.1 

; 

Hot           Cold 

Hot            Cold 

(6)  If  there  is  time  for  it,  the  substances  in  (a)  may  be 
tested  in  beads  made  with  microcosmic  salt,  in  exactly  the 
same  way. 

In  any  case,  make,  with  a  clean  bead  from  microcosmic  salt 
and  a  0.5  mm.  bit  of  orthoclase,  the  test  for  a  silicate.  The  in- 
soluble residue  which  swims  in  the  bead  has  the  same  compo- 
sition as  quartz  (Si02).  It  is  called  the  "silica-skeleton." 

(c)  is  a  suggested  list  of  three  minerals  in  which  you  are  to 
identify  the  metal  by  the  borax  bead  color  in  oxidizing  and 
reducing  flames.  Also  determine  whether  the  substance  is  a 
silicate  or  carbonate. 


1  The  abbreviations  O.F.  and  R.F.  are  used  for  oxidizing  flame  and  re- 
ducing flame. 


92  LABORATORY   STUDIES   IN   CHEMISTRY 

EXERCISE  64 ! 
DYEING 

Apparatus.  —  Seven  agate  pans.  Liter  flask  for  roughly  measuring 
water.  Glass  rod.  Trip  scales. 

Materials.  —  Cotton  cloth  (white).  Flannel  (white).  Congo  red. 
Aniline  red.  Malachite  green.  Distilled  water.  Sodium  carbonate. 
Sodium  sulphate.  Tannic  acid.  Tartar  emetic.  Large  gummed 
labels  (Dennison's,  No.  201).  Paste. 

Method.  —  See  textbook,  page  234. 


Preparation  of  the  cloth. — Cut  into  strips  4x2  cm.  (1.6  X 
0.8  in.).  Each  student  will  need  2  pieces  of  the  flannel  and  5 
of  the  cotton.  The  sizing  must  be  removed  from  the  cotton 
by  boiling  it  in  an  agate  pan  with  a  mixture  of  40  c.c.  concen- 
trated hydrochloric  acid  and  1  liter  tap  water,  rinsing  under 
the  hydrant  and  then  dipping  in  a  cold  mixture  of  10  c.c.  am- 
monia and  1  liter  tap  water.  This  treatment  is  not  necessary 
with  the  flannel. 

B 

Prepare  the  following  baths :  — 

(1)  1  gram  Congo  red  is  dissolved  by  stirring  in  1  liter  of 
distilled  water  in  an  agate  pan.     Add  1  gram  sodium  carbon- 
ate and  2  grams  sodium  sulphate. 

(2)  0.5  gram  aniline  red  in  1  liter  distilled  water. 

(3)  0.5  gram  malachite  green  in  1  liter  distilled  water. 

(4)  1  gram  tannic  acid  in  1  liter  distilled  water. 

(5)  1  gram  tartar  emetic  in  1  liter  distilled  water. 

(1),  (2),  (3),  and  (4)  are  heated  to  gentle  boiling.  (5)  should 
be  cold.  Each  pan  should  be  plainly  labeled  with  its  number. 

1  In  order  to  finish  in  a  laboratory  period,  it  will  be  necessary  to  dis- 
tribute the  preparation  of  the  baths  to  different  students. 


DYEING  93 


(a)  Wet  a  strip  of  cotton  cloth,  place  it  in  (1)  (gentle  boil- 
ing), and  move  it  about  with  a  glass  rod  for  one  minute.  Re- 
move and  wash  well  under  the  tap.  Congo  red  belongs  to  the 
class  of  dyes  which  dye  cotton  without  a  mordant.  Fasten  the 
dyed  cloth  to  your  notebook  page. 

(6)  Place  a  second  strip  of  cotton  cloth  in  (2)  and  a  third  in 
(3)  for  one  minute.  Eemove  and  wash  well.  Eesult  ?  Aniline 
red  and  malachite  green  are  examples  of  a  great  class  of  dye- 
stuffs  which  do  not  give  fast  colors  on  cotton  without  the  use 
of  a  mordant. 

(c)  Boil  two  strips  of  cotton  cloth  in  (4)  for  five  minutes. 
Wring  out  and  keep  in  motion  in  (5)  for  five  minutes.     Now 
place  one  strip  in  (2)  and  move  about  constantly  for  one  min- 
ute.    Treat  the  other  similarly  in  (3).     Try  to  wash  out  the 
color.   Eesult  ?  What  part  is  played  by  the  mordant  (4  and  5)  ? 
Mount  the  dyed  cloth  on  your  notebook  page. 

(d)  Stir  a  strip  of  flannel  in  (2)  and  a  second  in  (3)  for  one 
minute,  without  mordanting.    Eemove  and  try  to  wash  out  the 
color.     What  difference  do  you  discover  in  the  action  of  wool 
and  of  cotton  toward  dyes  of  the  class  to  which  aniline  red  and 
malachite  green  belong  ?     Mount  the  dyed  cloth  on  the  note- 
book page. 

Thoroughly  wash  the  pans,  using  a  little  concentrated 
hydrochloric  acid,  if  necessary,  to  remove  the  dyestuff. 


94 


LABORATORY    STUDIES   IN    CHEMISTRY 


EXERCISE   65 

NITRIC   ACID,   AQUA   REGIA 

Apparatus.  —  Retort  (150  c.c.)  with  glass  stopper.  Agate  pan. 
Beaker.  Small  test  tubes.  Trip  scales.  Glass  rod.  Mortar  and 
pestle.  Manila  paper. 

Materials.  —  Sodium  nitrate.  Mossy  zinc.  Magnesium  ribbon. 
Iron  filings.  Tin  foil.  Colored  cloth  of  any  kind.  Gold  leaf.  Fer- 
rous sulphate.  Manila  paper. 

Method.  —  See  textbook,  page  297. 

CAUTION:  The  gases  given  off  ivhen  nitric  acid  acts  upon  metals 
and  the  vapor  of  nitric  acid  itself  are  poisonous  and  must  not  be  inhaled. 
Do  not  get  nitric  acid  upon  the  skin  or  clothing. 

(a) 1  Fit  up  the  apparatus  shown  in  Fig.  21.  Roughly  weigh 
on  the  trip  scales  enough  sodium  nitrate  to  fill  the  retort  about 

one  third.  Weigh  off 
in  a  beaker  an  equal 
quantity  of  concen- 
trated sulphuric  acid. 
Introduce  the  sodium 
nitrate  into  the  retort 
by  means  of  a  piece 
of  paper.  Add  the 
sulphuric  acid,  insert 
the  glass  stopper  (not 
a  rubber  or  wooden 
cork,  which  would  be 
rapidly  destroyed  by 
the  nitric  acid),  and 
heat  gently.  Only 
FIG.  21.  vapor,  not  solid  or 

liquid,  must  pass  over. 
Why  ?     Empty  the  liquid  which  remains  in  the  retort  into  the 

1  If  the  period  is  short,  it  may  be  necessary  to  omit  or  to  postpone  (&) 
and  (c). 


NITRIC  ACID,  AQUA  REGIA  95 

vessel  provided  for  the  purpose.  (Care!}  When  the  retort  is 
cold,  half  fill  it  with  water  and  boil  gently  to  clean  it. 

Examine  the  nitric  acid  which  collects  and  record  its  prop- 
erties. Use  the  nitric  acid  in  the  following  experiments. 
Cover  a  piece  of  zinc  with  water  in  a  test  tube  and  slowly  add 
nitric  acid.  Do  the  same  thing  with  a  little  iron  filings  and  a 
piece  of  magnesium.  In  these  reactions  water  is  produced,  to- 
gether with  the  nitrate  of  the  metal  used.  The  gas  produced 
may  be  nitrous  oxide,  nitric  oxide,  or  nitrogen  peroxide,  accord- 
ing to  the  temperature  and  strength  of  the  acid.  Do  not  try  to 
write  the  equations,  which  are  quite  difficult.  Simply  remem- 
ber the  general  character  of  the  action  and  the  way  in  which  it 
differs  from  the  action  of  sulphuric  or  hydrochloric  acid  on  the 
same  metals  (see  textbook,  page  298). 

Drop  a  fragment  of  tin  into  concentrated  nitric  acid  in  a  test 
tube.  The  metal  is  converted  into  tin  oxide  by  the  oxygen  of 
the  nitric  acid.  Let  a  drop  of  nitric  acid  fall  upon  a  colored 
fabric  of  any  kind. 

(b)  Aqua  regia.  —  Pick  up  a  small  piece  of  gold  leaf  with  the 
end  of  a  wet  glass  rod,  and  rinse  it  into  a  test  tube  with  water. 
In  the  same  way  place  another  piece  of  gold  leaf  in  another 
test  tube.     Add  to  one  tube  nitric  acid  and  to  the  other  hydro- 
chloric acid.    Heat  both  tubes.    Does  the  gold  dissolve  ?   Pour 
the  contents  of  either  tube  into  the  other,  and  go  on  heat- 
ing. (?)     The  product  is  gold  chloride,  and  the  gold  dissolves 
because  the  oxygen  of  the  nitric  acid  liberates  chlorine  from 
the  hydrochloric  acid  and  the  chlorine  attacks  the  gold.     The 
mixture  of  nitric  and   hydrochloric   acids   will   also  dissolve 
platinum. 

(c)  Test  for  nitric  acid   or  a  nitrate   (N03  ions).  —  Exercise 
unusual  care  in  following  directions.  —  Select  2  c.c.  of  clean 
ferrous   sulphate  crystals,  wash  in  running  water,  dry  with 
paper  (manila),  and  powder  in  a  clean  mortar.    Shake  the  pow- 
der  with  10  c.c.  water   (no  heat)    until   you    have   a   strong 
solution. 

Place  3  c.c.  of  the  clear  liquid  in  a  small  test  tube,  incline 


96          LABORATORY   STUDIES   IN   CHEMISTRY 

the  tube  at  an  angle  of  45°,  and  allow  5  c.c.  strong  sulphuric 
acid  to  trickle  slowly  down  the  side.  Avoid  shaking.  Being 
denser,  the  acid  will  form  a  layer  below  the  solution. 

Now,  add  in  the  same  way,  a  few  drops  of  nitric  acid  which 
has  been  diluted  with  twenty  times  its  volume  of  water, 
Eesult? 

Repeat,  using  a  few  drops  of  sodium  nitrate  solution  about 
1:20. 

•  If  time  permits,  repeat,  using  other  nitrates  (e.g.  potassium 
nitrate,  ammonium  nitrate)  to  show  that  the  test  is  for  NO3 
ions  in  general,  not  for  any  special  nitrate. 

/  » 

EXERCISE   66 

POTASSIUM  NITRATE 

Apparatus.  —  Evaporating  dish.  Glass  plate.  Funnel.  Beaker. 
Lens.  Wire  gauze.  Trip  scales.  Glass  rod.  Graduated  cylinder. 

Materials.  —  Sodium  nitrate.  Potassium  chloride.  Potassium 
nitrate  crystals.  Silver  nitrate  solution.  Distilled  water.  Filters. 

Method.  —  See  textbook,  page  301. 

Place  in  a  dish  25  c.c.  water.  Add  12  grams  sodium  nitrate 
and  11  grams  potassium  chloride.  Heat  on  wire  gauze,  stirring 
with  a  glass  rod  until  both  are  completely  dissolved. 

Stir  gently  and  continue  heating  until  half  the  water  has 
evaporated  (small  flame).  Pour  off  the  clear  liquid  into  a 
beaker  and  let  it  stand  until  cool.  Meanwhile,  scrape  the 
crystals  left  in  the  dish  into  a  filter  supported  in  a  funnel. 
Press  carefully  with  the  rod  so  as  to  squeeze  out  as  much  of 
the  liquid  as  possible.  Put  a  few  crystals  on  a  glass  plate 
and  examine  with  a  lens  or  low-power  microscope.  What  is 
the  form  ?  Only  four  substances  might  be  obtained  from  your 
solution  in  this  way.  What  are  they?  Which  of  them  do 
you  know  to  crystallize  in  the  form  you  have  observed  (text- 
book, page  206).  Taste  the  crystals  (a  trace  only),  Does  the 
taste  confirm  your  opinion  ? 


PREPARATION  OF  SODIUM  NITRITE  97 

Examine  the  crystals  which,  have  separated  in  the  beaker 
and  treat  them  in  the  same  way.  Compare  them  with  the 
crystals  of  potassium  nitrate  in  the  stock  bottle.  Use  the  lens 
or,  if  necessary,  the  microscope. 

Look  up  the  solubility  curves  of  sodium  chloride  and  of 
potassium  nitrate  at  different  temperatures  (textbook,  page 
207). 

Why  did  the  sodium  chloride  separate  while  the  liquid  was 
hot  ?  Why  did  the  potassium  nitrate  remain  dissolved  until 
the  liquid  cooled  ? 

Does  your  potassium  nitrate  contain  any  sodium  chloride  as 
an  impurity  (look  again  at  the  solubility  curve  for  sodium 
chloride)?  Verify  your  prediction  by  dissolving  0.5  c.c.  of 
your  potassium  nitrate  in  distilled  water  and  testing  the  solu- 
tion for  chloride  with  one  drop  of  silver  nitrate  solution. 
Eeserve.  Dissolve  the  rest  of  your  potassium  nitrate  in  10  c.c. 
hot  water  and  allow  the  solution  to  cool  and  crystallize.  Test 
again  with  silver  nitrate.  Is  the  second  crop  of  crystals  purer 
than  the  first  ?  Why  ? 

EXERCISE  67 
PREPARATION   OF   SODIUM  NITRITE 

Apparatus.  —  Iron  dish.  Beaker.  Evaporating  dish.  Funnel. 
Glass  rod.  Two  small  test  tubes.  Trip  scales. 

Materials.  —  Sodium  nitrate.     Lead  foil  or  test  lead.     Filters. 
Method.  —  See  textbook,  page  305. 

Melt  10  grams  sodium  nitrate  in  an  iron  dish  and  heat  it 
strongly  (take  special  care  not  to  spill  any  of  the  melted  sub- 
stance upon  the  table,  since  it  would  burn  deeply  into  the 
wood).  Add  gradually  20  grams  of  test  lead  (granulated)  or 
the  same  weight  of  lead  foil  cut  into  small  pieces.  Stir  with 
a  glass  rod  and  continue  heating  and  stirring  until  the  metal 
has  almost  completely  disappeared.  Let  cool. 

Meanwhile,  boil  30  c.c.  of  water  in  a  beaker  and  pour  it 


98          LABORATORY   STUDIES   IN   CHEMISTRY 

upon  the  cold  substance  in  the  iron  dish.  Boil  for  a  short 
time  and  filter,  receiving  the  filtrate  in  a  porcelain  dish. 
Evaporate  carefully  to  small  volume  and  let  it  crystallize. 
The  product  is  sodium  nitrite. 

Compare  it  with  sodium  nitrate.  Is  there  any  difference  in 
color?  Dissolve  1  c.c.  of  each  in  5  c.c.  water  and  cautiously 
add  1  c.c.  strong  sulphuric  acid.  Results  ? 

What  is  the  purpose  of  adding  the  lead  ?  What  substance 
remained  on  the  filter  ? 

EXERCISE  68  * 
NITRIC   OXIDE 

Apparatus.  —  Gas-generating  bottle  with  thistle  tube  and  delivery 
tube.  Test  tube.  Agate  pan.  Iron  spoon.  Three  bottles.  Glass  plates  or 
filter  paper  for  covering  bottles.  Watch  glass.  Beaker.  Wire  gauze. 

Materials.  —  Copper  clippings  (No.  12  wire  cut  into  1  cm.  pieces  is 
suitable).  Iron  wire.  Candles.  Sulphur.  Red  phosphorus.  Asbes- 
tos paper. 

Method.  —  See  textbook,  pages  298,  299,  304. 

CAUTION:  Nitric  oxide  is  poisonous.  Keep  the  bottles  of  the  gas 
covered  during  combustions  and  let  the  products  escape  out  of  the  windows. 

Nitric  oxide  is  made  in  the  same  apparatus  which  is  used 
for  generating  hydrogen.  Fill  the  generator  to  the  depth  of 
about  1  cm.  with  copper  clippings  or  cut  pieces  of  sheet  cop- 
per. In  another  bottle,  dilute  50  c.c.  nitric  acid  with  twice  its 
volume  of  water.  Cool  this  liquid  and  pour  it  upon  the  copper 
until  the  generator  is  one  third  filled.  Make  sure  that  the 
thistle  tube  dips  into  the  liquid.  Collect  the  gas  over  water. 
It  is  well  to  stand  the  generator  in  cold  water.  If  the 
evolution  of  gas  becomes  too  energetic,  pour  a  little  water 
down  the  thistle  tube.  Collect  three  bottles  and  one  test  tube 
of  the  gas.  Then  stop,  as  even  the  first  gas  which  comes  off  is 
not  quite  pure  and  the  later  portions  contain  large  quantities 

1  Two  students  can  work  together  to  advantage. 


NITROUS  OXIDE  99 

of  nitrous  oxide  and  other  impurities.  Leave  the  bottles  stand- 
ing in  the  water. 

Disconnect  the  apparatus  (do  not  inhale  the  gas)  and  pour  a 
little  of  the  blue  liquid  into  a  watch  glass.  Use  the  watch 
glass  as  a  cover  for  a  beaker  half  filled  with  water  kept  gently 
boiling.  Let  the  blue  liquid'  evaporate  almost  to  dryness. 
What  is  the  product  ?  Wash  off  the  copper  in  the  generator 
and  return  what  is  left  of  it  to  the  stock  bottle. 

Use  the  test  tube  of  the  gas  to  investigate  its  solubility  in 
water.  Expose  a  bottle  of  nitric  oxide  to  the  air.  Eesult  ? 

Slip  aside  the  cover  of  a  bottle  and  plunge  to  the  bottom  of 
the  bottle  some  sulphur  burning  vigorously  in  a  spoon  lined 
with  asbestos  paper.  Remove  the  sulphur  at  once,  keeping 
the  bottle  covered,  and  do  the  same  thing  with  a  lighted  can- 
dle. Why  should  the  candle  be  placed  in  the  bottom  of  the 
bottle  ?  Interpret  the  results. 

Reline  the  spoon,  fill  it  with  red  phosphorus,  ignite,  and 
plunge  into  a  bottle  of  the  gas.  Result  ?  Before  putting 
away  the  spoon,  heat  it  to  redness  to  burn  out  any  unused 
phosphorus. 

EXERCISE   69  * 
NITROUS   OXIDE 

Apparatus.  —  Large  test  tube  with  rubber  stopper  and  delivery 
tube,  connected  as  shown  in  cut.  Four  bottles.  Two  small  test 
tubes.  Agate  pan.  Iron  spoon.  Glass  plates  or  filter  paper  for 
covering  bottles. 

Materials.  —  Ammonium  nitrate.  Christmas-tree  candles.  Iron 
wire.  Sulphur.  Red  phosphorus.  Wooden  splints.  Asbestos  paper. 

Method.  —  See  textbook,  page  303. 

Fill  a  large  test  tube  one  third  with  ammonium  nitrate. 
Clamp  it  at  an  angle  of  45°,  and  insert  a  perforated  stopper 
with  a  delivery  tube.  It  is  advisable,  though  not  absolutely 

1  Two  students  can  work  together  to  advantage. 


100        LABORATORY   STUDIES   IN   CHEMISTRY 


necessary,  to  pass  the  gas  through  an  empty  large  test  tube 
closed  by  a  doubly  perforated  stopper  before  collecting  it. 

The  apparatus  is 
shown  in  Fig.  22. 
Apply  a  gentle  heat 
and  collect  the  gas 
over  warm  water. 
The  evolution  of  gas 
must  be  slow  —  a 
bubble  or  two  a  sec- 
ond. If  it  becomes 
too  rapid,  explosions 
result.  This  can  be 
easily  controlled  by 
lowering  or  remov- 

FlG  22  inS  the  flame.     Stop 

heating  and  remove 

the  stopper  before  the  ammonium  nitrate  is  exhausted.  Ex- 
plosions sometimes  occur  when  the  quantity  of  substance  becomes 
small.  If  the  ammonium  nitrate  shows  signs  of  giving  out  be- 
fore you  have  enough  gas,  disconnect,  add  more  ammonium 
nitrate  directly  to  the  liquid  in  the  test  tube,  and  resume  heat- 
ing cautiously.  Is  there  evidence  of  the  formation  of  any 
product  besides  the  gas  ?  What  ? 

Collect  four  bottles  and  two  test  tubes  full  of  the  gas.  Cover 
the  bottles  with  glass  plates  or  wet  filter  paper,  and  stand 
them  upright  on  the  desk.  Use  one  bottle  to  determine  color, 
odor,  and  taste.  Try  the  spark  test  in  the  test  tube.  Ascer- 
tain if  the  gas  is  soluble  in  water.  Plunge  a  lighted  candle 
into  a  bottle  of  it.  Result?  Set  fire  to  some  sulphur  in  a 
deflagration  spoon  lined  with  asbestos  paper,  and  at  the  instant 
the  sulphur  begins  to  burn  plunge  it  into  the  third  bottle  of 
nitrous  oxide.  It  should  be  extinguished.  Cover  the  bottle, 
and  heat  the  sulphur  until  it  burns  vigorously.  Plunge  it 
again  into  the  gas.  Result  ?  Is  nitrous  oxide  easy  or  diffi- 
cult to  decompose  into  its  elements  ?  Which  has  probably 


PHOSPHATE   FERTILIZERS?  ;'j,  J':  ;*, ;  \  # 


the  higher  temperature,  the  candle  flame  or  the  flame  of  burn- 
ing sulphur?  Remove  the  asbestos  and  reline  the  spoon. 
Fill  it  with  red  phosphorus,  ignite,  and  plunge  into  a  bottle  of 
the  gas.  Result  ? 

EXERCISE  70 
PHOSPHATE   FERTILIZERS 

Apparatus.  —  Porcelain  dish.   Small  test  tubes.   Glass  rod.   Funnel. 

Materials.  —  Sodium  hydrogen  phosphate  (Na2HPO4).  Ammo- 
nium nitrate.  Ammonium  molybdate  solution.  Apatite  or  phos- 
phate rock.  Commercial  superphosphate.  Filters. 

Method.  —  See  textbook,  page  331. 

(a)  Dissolve  in  a  small  test  tube  0.5  c.c.  sodium  hydrogen 
phosphate  and  1  c.c.  ammonium  nitrate  in  5  c.c.  water,  and  add 
five  drops  of  nitric  acid.     Add  2  c.c.  ammonium   molybdate 
solution   and  warm   gently,  not  to   boiling.      Result?      The 
composition  of  the  product  depends  upon  the  temperature,  so 
that  no  formula  can  be  assigned  to  it. 

This  is  the  test  for  phosphoric  acid,  or  a  soluble  phosphate 

(that  is,  for  PO^ions). 

(b)  Place  10  grams  powdered  apatite  or  phosphate  rock  in  a 
dish  and  add  4  c.c.  water  and  4  c.c.  concentrated  sulphuric 
acid.     Warm  for  ten  minutes,  stirring  with  a  glass  rod.     Add 
10  c.c.  water,  warm,  filter,  and  test  the  clear  liquid  as  in  (a), 
omitting  the  sodium  hydrogen  phosphate.     Has  the  action  of 
the  sulphuric  acid  on  the  mineral  produced  a  soluble  phos- 
phate ?     Explain  (see  textbook,  p.  331).* 

(c)  Clean   the  dish,  place  2  c.c.  superphosphate  in  it,  add 
50  c.c.  water,  and  boil.     Filter  and  test  as  in  (6).     Result? 
Does  the  fertilizer  contain  a  soluble  phosphate  ?     What  is  the 
object  of  the  sulphuric  acid  in  its  manufacture  ? 


102         L/IB^RATGRY  STUDIES   IN  CHEMISTRY 

EXERCISE   71 l 

POTASSIUM   CHROMATE   AND   POTASSIUM 
DICHROMATE 

Apparatus. — Graduated  100  c.c.  cylinder.  Trip  scales.  Beaker. 
Evaporating  dish.  Three  small  test  tubes. 

Materials.  —  Potassium  hydroxide.  Potassium  dichromate.  Potas- 
sium chromate.  Dilute  solutions  of  barium  chloride,  lead  nitrate  and 
silver  nitrate.  The  potassium  dichromate  should  be  powdered  to 
hasten  solution. 

Method.  — See  textbook,  pages  342  and  343. 

(a)  Calculate  the  molecular  weight  of  potassium  dichromate. 
Using  decigrams  as  your  unit,  weigh  off  one  fourth  of  the 
molecular  weight  and  dissolve  it  in  50  c.c.  water  in  a  dish, 
using  gentle  heat,  if  necessary.  From  the  equation  — 

K2Cr2O7         +2KOH->         2  K2CrO4       +  H2O, 

(Potassium  dichromate)  (Potassium  chromate) 

calculate  the  quantity  of  potassium  hydroxide  which  would  be 
required  to  interact  with  the  potassium  dichromate.  Weigh 
off  this  quantity,  dissolve  it  in  10  c.c.  water,  and  add  it  to  the 
solution  of  the  dichromate.  What  does  the  color  change  indi- 
cate ? 

Estimate  roughly  how  far  the  solution  must  be  evaporated 
in  order  to  deposit  three  fourths  of  its  potassium  chromate  on 
cooling.  Calculate  the  quantity  of  potassium  chromate  from 
the  equation  above.  Assume  that  1  c.c.  water  dissolves  two 
thirds  of  a  gram  of  potassium  chromate  at  room  temperature. 

Evaporate  the  solution  as  far  as  you  think  it  is  necessary 
and  let  it  cool.  Meanwhile,  go  on  with  (c).  If  you  do  not  ob- 
tain a  good  crop  of  crystals,  evaporate  further  and  find  the 
error  in  your  calculation.  Examine  the  crystals  and  compare 
them  with  potassium  dichromate. 

1  If  the  laboratory  period  is  short,  two  students  can  work  together  to 
advantage. 


POTASSIUM  CHROMATE  103 

* 

(6) l  Your  dish  must  contain  one  half  the  molecular  weight 
of  potassium  chromate,  measured  in  decigrams.  Why  ?  Cal- 
culate the  quantity  of  sulphuric  acid  required  to  interact  with 
this  according  to  the  equation :  — 

2  K2CrO4  +  H2SO4  — >-  K2Cr2O7  +  K2SO4  +  H2O. 

Dissolve  the  potassium  chromate  in  50  c.c.  water  and  slowly 
add  the  calculated  quantity  of  sulphuric  acid,  stirring.  What 
does  the  change  in  color  indicate  ?  If  8  parts  water  dis- 
solve 1  part  potassium  dichromate  at  room  temperature,  how 
far  must  you  evaporate  in  order  to  allow  three  fourths  of 
the  substance  to  crystallize  on  cooling  ?  To  answer  this,  you 
must  know  the  amount  of  potassium  dichromate  in  the  liquid. 
Is  it  necessary  to  calculate  this  ?  Why  ?  Evaporate  to  the 
volume  estimated  and  let  the  solution  crystallize. 

(c)  Dissolve  1  c.c.  potassium  dichromate  in  20  c.c.  water. 
In  three  separate  test  tubes  (small),  investigate  the  behavior  of 
the  solution  with  solutions  of  barium  chloride,  lead  nitrate,  and 
silver  nitrate.  Use  not  more  than  5  c.c.  of  each  solution. 

The  precipitates  are  the  chromates  of  the  corresponding 
metals.  Record  their  properties  and  see  whether  they  dis- 
solve in  nitric  acid. 

1  If  the  laboratory  period  is  short,  (6)  can  be  assigned  to  a  second  stu- 
dent and  started  simultaneously  with  (a).  Use  one  half  the  molecular 
weight  of  potassium  chromate,  taking  decigrams  as  the  unit. 


104        LABORATORY    STUDIES   IN   CHEMISTRY 

EXERCISE  72 
AMMONIUM  BICHROMATE 

Apparatus.  —  Four  small  test  tubes,  one  of  which  must  be  dry. 
Glass  rod. 

Materials.  —  Solid  ammonium  dichromate  (NH4)2Cr2O7.  Solutions 
of  barium  chloride,  lead  nitrate  and  silver  nitrate.  Potassium  hydrox- 
ide solution.  Red  litmus  paper. 

Method.  —  The  chemical  behavior  of  a  substance  when  ionized  and  when 
not  ionized  is  very  different. 

(a)  Repeat  (c)  of  the  preceding  exercise,  using  ammonium 
dichromate  instead  of  the  potassium  salt. 

To  5  c.c.  ammonium  dichromate  solution  add  ammonium 
hydroxide  until  the  color  change  is  complete.  Does  it  behave 
like  potassium  dichromate  ?  What  must  have  been  formed  ? 
Equation  ? 

(6)  To  5  c.c.  ammonium  dichromate  solution  add  potassium 
hydroxide  solution  until  the  color  is  pure  yellow.  Then  add 
as  much  more  potassium  hydroxide  and  heat  gently.  Note 
odor.  Test  the  gas  with  red  litmus  paper.  With  a  rod  wet 
with  concentrated  hydrochloric  acid.  What  is  it  ? 

Ammonium  dichromate  in  water  solution  is  largely  ionized 

to  NH4,  NH4,  and  Cr267.  Accordingly,  like  other  salts  it 
yields  two  classes  of  reactions,  those  of  the  ion  NH4,  of  which 
(6)  is  an  example ;  and  those  of  the  ion  Gr/)ri  of  which  various 
examples  are  met  in  (a). 

(c)  Now  investigate  the  conduct  of  the  un-ionized  substance. 
Place  1  c.c.  of  the  crystals  in  a  dry  test  tube  and  heat  gently. 
Stop  heating  when  the  action  begins,  but  resume  heating,  if 
necessary,  to  complete  it.  Hold  the  tube  with  a  paper  holder 
or  a  clamp.  The  chief  products  are  nitrogen,  water  (steam), 
and  chromic  oxide  (solid). 

(NH4)2Cr207  ->  Cr203  +  4  H2O  +  N2. 

Note  that  this  decomposition  is  totally  different  from  the 
reactions  of  the  same  substance  in  water  solution.  In  the 


CHROMIUM   IN  AMMONIUM   BICHROMATE     105 

latter  case  it  behaves  as  though  the  NH4  and  Cr207  had  parted 
company  and  gives  a  different  set  of  reactions  for  each,  much 
as  a  solution  containing  both  copper  and  silver  ions  will  give 
the  tests  for  both  metals.  In  (c)  there  is  no  evidence  of  this 
separation.  The  formation  of  water  indicates,  for  instance, 
that  the  hydrogen  and  the  oxygen  are  in  the  same  molecule. 
Examine  the  chromic  oxide  carefully  and  test  its  solubility 
in  hydrochloric  acid. 


EXERCISE  73 

THE   PERCENTAGE  OF   CHROMIUM  IN 
AMMONIUM   BICHROMATE 

(Quantitative) 

Apparatus.  —  Porcelain  crucible  and  cover.  Pipestem  triangle. 
Balance. 

Material.  —  Ammonium  dichromate. 

Method.  —  When  ammonium  dichromate  is  heated,  the  following 
change  occurs :  — 

(NH4)2Cr2O7  ->  Cr2O3  +  N2  +  4  H2O. 

(Ammonium  dichromate)    (Chromic  oxide) 

The  percentage  of  chromium  in  the  sample  can  be  calculated  from 
the  weight  of  the  chromic  oxide  left  in  the  crucible. 

Clean  and  weigh  crucible  and  cover.  Place  cover  on  balance 
pan  beside  crucible  and  weigh  in  the  crucible  0.5  gram  am- 
monium dichromate.  Cover  crucible,  place  it  on  the  triangle, 
and  heat  cautiously  with  a  small  flame  kept  in  motion.  Hold 
down  the  lid  for  the  first  few  minutes  by  placing  the  tip  of 
your  pencil  through  the  ring.  If  any  noise  is  heard  or  any 
smoke  appears,  stop  heating  for  a  moment  until  quiet  is 
restored.  Finally  remove  pencil  and  apply  the  full  heat  of 
the  burner  for  ten  minutes ;  cool  and  weigh  without  removing 
cover. 


106        LABORATORY   STUDIES   IN   CHEMISTRY 

V 

Calculation.  —  The  weight  of  the  chromium  in  your  sample  is 
obtained  by  working  out  the  following  fraction  :  — 

weigh  chromic  oxide  x  twice  the  atomic  weight  chromium 
molecular  weight  chromic  oxide 

The  percentage  of  chromium  is :  — 

weight  chromium  x  100 
0.5 


EXERCISE  74 

THE  PERCENTAGE   OF  IRON   IN  FERROUS 

AMMONIUM   SULPHATE 

[FeS04(NH4)2S04  6  H2O] 

(Quantitative) 

Apparatus.  —  Burette.  Beaker.  Stirring  rod  (thin,  3  mm.  diam- 
eter. Thick  rods  cause  breakage  of  beakers).  Graduated  cylinder. 
Balance. 

Materials.  —  Ferrous  ammonium  sulphate.  Distilled  water.  A 
solution  of  potassium  permanganate,  KMnO4,  of  such  strength  that 
1  c.c.  corresponds  to  0.01  gram  of  iron.  This  solution  is  made  by 
dissolving  5.643  grams  of  potassium  permanganate  in  water  and 
diluting  the  solution  to  1  liter  in  a  flask  with  a  mark  on  the  neck. 
The  student  can  prepare  the  solution  by  dissolving  0.564  gram  of 
potassium  permanganate  in  50  c.c.  distilled  water  in  a  beaker.  Make 
sure  that  the  permanganate  is  completely  dissolved.  Pour  into  a  gradu- 
ated cylinder,  and  wash  the  beaker  with  5  c.c.  distilled  water,  which 
is  poured  into  the  cylinder.  Repeat  the  washing  three  times.  Dilute 
with  distilled  water  to  exactly  100  c.c.  and  mix  thoroughly. 

Method.  —  In  presence  of  sulphuric  acid,  potassium  permanganate 
converts  ferrous  sulphate,  FeSO4,  into  ferric  sulphate,  Fe2(SO4)3, 
thus  :  — 

10  FeSO4  +  2  KMnO4  +  8  H2SO4  ->  5  Fe2(SO4)3  -t-  K2SO4 


Weigh  in  a  dry,  clean  beaker  2  grams  of  ferrous  ammonium 
sulphate,  half  fill  the  beaker  with  distilled  water,  and  stir  until 


SODIUM  CHLORIDE  107 

the  solid  is  completely  dissolved.    Do  not  heat.    Add  3  c.c.  con- 
centrated sulphuric  acid. 

Fill  the  burette  to  zero  with  the  permanganate  and  stand  the 
beaker  on  a  piece  of  white  paper.  Slowly  run  in  the  perman- 
ganate, stirring  constantly.  When  the  purple  color  seems  to 
spread  through  the  liquid  in  the  beaker  before  disappearing, 
you  are  near  the  end,  and  the  permanganate  should  be  added 
one  drop  at  a  time  ;  stirring  after  each.  The  first  perceptible 
color  which  remains  after  stirring  a  few  seconds  indicates 
that  the  change  is  complete.  If  in  doubt,  record  the  reading 
and  add  another  drop.  If  the  color  becomes  more  intense,  the 
previous  reading  was  the  end. 

Calculation.  —  The  reading  of  the  burette  x  0.01  =  weight  of  iron 
in  sample. 

weight  of  iron  in  sample  x  100 

2 2 —  =  percentage  of  iron. 


EXERCISE  75 

DETERMINATION   OF   THE   PERCENTAGE   OF 
CHLORINE  IN   SODIUM  CHLORIDE 

(Quantitative) 

Apparatus.  —  Burette.  Small  test  tubes.  Beaker.  Stirring  rod 
(thin,  3  mm.  diameter).  Balance. 

Materials.  —  Pure  sodium  chloride.  Decinormal  (one-tenth  normal) 
silver  nitrate  solution  (made  by  dissolving  17  grams  silver  nitrate  in 
distilled  water  and  diluting  to  1  liter  in  a  volumetric  flask).  The 
student  can  prepare  the  solution  by  dissolving  exactly  1.7  gram  of 
silver  nitrate  in  distilled  water  in  a  graduated  cylinder,  diluting  to 
100  c.c.  and  mixing  thoroughly.  Solution  of  potassium  chromate 
(20  grams)  in  distilled  water  (1  liter).  Potassium  chloride  and 
potassium  bromide  are  optional. 

Method.  —  Dissolve  a  crystal  of  sodium  chloride  in  5  c.c.  distilled 
water  in  a  clean  test  tube  and  add  a  few  drops  of  silver  nitrate  solu- 
tion. In  another  tube,  mix  1  c.c.  of  silver  nitrate  solution  with  1  c.c. 


108       LABORATORY   STUDIES   IN   CHEMISTRY 

of  potassium  chromate  solution.  The  red  precipitate  is  silver  chro- 
mate :  — 

2  AgNO3  +  K2Cr04  ->  Ag2CrO4  +  2  KNO3. 

Now  when  silver  nitrate  solution  is  dropped  into  a  liquid  containing 
both  sodium  chloride  and  potassium  chromate,  silver  chloride  only  is 
formed  as  long  as  any  chlorine  ions  remain.  When  the  chlorine  ions 
are  all  converted  into  silver  chloride,  the  first  drop  of  silver  nitrate  in 
excess  gives  the  red  color  of  silver  chromate. 

Weigh  0.2  gram  of  sodium  chloride  in  a  clean,  dry  beaker, 
dissolve  in  50  c.c.  distilled  water,  and  add  2  c.c.  potassium 
chromate  solution.  Fill  the  burette  to  zero  with  the  silver 
nitrate.  Stand  the  beaker  on  white  paper  and  slowly  run  in 
the  silver  nitrate  solution,  stirring  constantly.  The  first  faint 
permanent  change  in  color  is  the  end.  When  in  doubt,  record 
the  reading  and  add  another  drop. 

Calculation.  — 

1  c.c.  decinormal  silver  nitrate  =  0.00355  gram  chlorine. 
and,  hence,  burette  reading  x  0.00355  =  weight  of  chlorine  in  sample ; 

burette  reading  x  0.00355x100  =  t        of  chlorine. 

0.2 

In  the  same  way,  determine  the  chlorine  in  potassium 
chloride,  taking  0.3  gram. 

In  the  same  way,  determine  the  bromine  in  potassium 
bromide,  taking  0.4  gram. 

1  c.c.  decinormal  silver  nitrate  =  0.008  gram  bromine. 


ANALYSIS  OF  A  SILVER  COIN  109 

EXERCISE  76 

ANALYSIS   OF  A   SILVER  COIN 

(Quantitative) 

Apparatus.  —  Balance.  Burette.  Graduated  cylinder.  Beaker. 
Thin  stirring  rod.  Watch  glass.  Test  tubes.  Tinner's  shears. 

Materials.  —  Silver  nitrate.  Silver  nitrate  solution.  Ammonium 
sulphocyanide  (NH4CNS).  Solution  of  ferric  ammonium  sulphate 
(Fe2(SO4)3(NH4)2SO424H2O),  twenty  grams  to  about  1  liter  of 
distilled  water.  Distilled  water. 

Method.  —  Dissolve  a  crystal  of  ammonium  sulphocyanide  in  10  c.c. 
distilled  water  and  divide  the  solution  in  two  portions.  To  one  por- 
tion add  a  few  drops  of  silver  nitrate.  The  white  precipitate  is  silver 
sulphocyanide :  — 

AgN03  +  NH4CNS  ->  AgCNS  +  NH4NO3. 

To  the  other  portion  add  a  few  drops  of  ferric  ammonium  sulphate. 
The  red  color  is  due  to  ferric  sulphocyanide,  formed  from  the  ferric 
sulphate  and  the  ammonium  sulphocyanide  :  — 

Fe2(S04)3  +  6  NH4CNS  ->  2  Fe(CNS),  +  3  (NH4)2SO4. 

(Ferric  sulphate)  (Ferric  sulphocyanide) 

Now  when  ammonium  sulphocyanide  is  added  slowly  to  a  liquid  con- 
taining both  silver  nitrate  and  ferric  sulphate,  silver  sulphocyanide 
only  is  formed  until  the  silver  is  all  precipitated  and  then  the  first  drop 
of  ammonium  sulphocyanide  in  excess  gives  the  liquid  the  red  color  of 
ferric  sulphocyanide  and  indicates  that  the  end  has  been  reached. 

In  a  graduated  cylinder,  dissolve  0.7  grain  ammonium  sul- 
phocyanide in  100  c.c.  distilled  water  and  mix  thoroughly. 
0.315  gram  of  pure  silver  nitrate  contaftis  just  0.2  gram  silver. 
Weigh  off  this  quantity  of  silver  nitrate  in  a  clean,  dry  beaker, 
dissolve  it  in  50  c.c.  distilled  water,  add  1  c.c.  nitric  acid  and 
1  c.c.  ferric  ammonium  sulphate  solution.1  Fill  the  burette  to 
zero  with  the  sulphocyanide  solution,  stand  the  beaker  on 

1  If  the  laboratory  period  is  short,  the  instructor  may  prefer  to  prepare 
a  large  quantity  of  the  sulphocyanide  solution  and  standardize  it  before- 
hand. The  experiment  then  requires  only  about  30  minutes. 


110        LABORATORY   STUDIES   IN   CHEMISTRY 

white  paper,  and  allow  the  sulphocyanide  to  run  in  until  the 
color  change  occurs.  Stir  constantly  and  add  the  sulphocyanide 
in  small  quantities.  Endeavor  to  hit  the  first  perceptible 
change.  When  in  doubt,  take  the  reading  and  add  another 
drop.  Plainly :  — 

o  P 

~ =  weight  of  silver  corresponding  to  1  c.c.  of  your 

sulphocyanide. 

Take  about  one  tenth  of  a  dime  for  the  analysis.  The  coin  can 
be  easily  cut  with  tinner's  shears.  Weigh  the  bit  of  coin  accu- 
rately, place  in  a  beaker,  and  add  2  c.c.  distilled  water  and 
2  c.c.  nitric  acid.  Cover  with  a  watch  glass,  place  on  wire 
gauze  and  put  a  small  flame  underneath. 

When  the  coin  is  dissolved,  add  50  c.c.  distilled  water  and 
1  c.c.  ferric  ammonium  sulphate  solution. 

Fill  the  burette  to  zero  with  the  sulphocyanide  and  proceed 
exactly  as  you  did  in  standardizing  your  solution. 

Calculation.  — 

burette  reading  x  silver  value  of  solution  x  100  _         cent  of   sijver 
weight  of  sample  ^  coin> 

EXERCISE  77 

THE  ATOMIC  WEIGHT   OF   COPPER  BY  REDUCING 
CUPRIC   OXIDE 

(Quantitative) 

Apparatus.  —  Hard  glass  test  tube  about  10  x  1.2  cm.  (4  x  0.5  in.) . 
Glass  tube  about  20  cm.  (8  in.)  long.  Rubber  tubing  for  connecting 
glass  tube  to  gas  supply.  Balance., 

Material.  —  Cupric  oxide  (this  should  have  been  heated  to  redness 
and  placed  in  a  stoppered  bottle). 

Method.  —  Cupric  oxide  when  heated  in  hydrogen  or  illuminating 
gas  is  converted  into  copper :  — 


The  atomic  weight  of  copper  is  obtained  from  the  loss  in  weight. 


ATOMIC  WEIGHT  OF  COPPER 


111 


The  hard  glass  tube  must  be  clean  and  dry.  Weigh  it  accu- 
rately. Cut  a  strip  of  paper  20x1  cm.  (8x0.4  in.)  and  crease 
it  in  the  middle  to  make  a  V-shaped  trough.  Use  this  to  intro- 
duce the  cupric  oxide.  Avoid  getting  the  latter  on  the  sides  of 
the  tube.  Weigh  in  the  tube  about  1  gram  of  cupric  oxide.  It 
is  not  necessary  to  take  exactly  1  gram,  but  whatever  quantity 
you  take  must  be  accurately  weighed. 

Connect  the  glass  tube  by  means  of  the  rubber  tube  to  the 
illuminating  gas  supply  and,  after  lighting  the  gas,  turn  it 
down  till  you  have  a  flame  about  15  mm.  (0.5  in.)  high.  Blow 
out  the  gas  and  set  up  the  apparatus  as  shown  in  cut  (Fig.  23). 
Place  the  clamp  2  cm.  (0.8  in.) 
from  the  mouth  of  the  tube  so 
that  you  may  heat  the  cupric 
oxide  without  burning  the 
clamp.  Light  the  gas  at  the 
mouth  of  the  test  tube.  Now 
heat  the  cupric  oxide  carefully 
and  keep  it  at  a  dull  red  heat 
for  five  minutes.  Let  cool 
slightly  and,  by  means  of  a 
towel,  turn  the  tube  until  the 
cupric  oxide  is  uppermost. 
Tap  with  a  pencil  until  the 
cupric  oxide  falls.  Heat  again 
to  redness  for  five  minutes. 
Remove  the  burner  for  five  minutes  ;  then  extinguish  the  flame 
at  the  mouth  of  the  tube ;  let  cool  and  weigh.  Place  the  copper 
in  the  receptacle  provided. 

Calculation.  —  The  loss  in  weight  is  oxygen.  The  weight  of 
the  copper  is  obtained  by  subtracting  the  weight  of  the  empty 
tube  from  the  weight  after  heating. 

weight  oxygen  :  weight  copper  : :  16  :  atomic  weight  copper. 


FIG.  23. 


112       LABORATORY   STUDIES   IN   CHEMISTRY 

EXERCISE  78 

PERCENTAGE  OF  COPPER  IN  COPPER  SULPHATE 
CRYSTALS 

(  Quantitative) 

Apparatus.  —  Same  as  in  Exercise  77. 
Material.  —  Copper  sulphate,  CuSO45  H2O. 

Method.  —  Copper  sulphate,  heated  in  illuminating  gas,  leaves  a 
residue  of  copper. 

Use  1  gram  of  finely  powdered  copper  sulphate  and  proceed 
exactly  as  in  Exercise  77.  Clamp  the  tube  near  the  mouth  and 
look  out  for  the  formation  of  water,  which  must  be  driven  out 
by  the  cautious  use  of  the  flame.  Have  the  tube  horizontal,  or 
the  water  will  run  back  into  the  heated  portion  and  produce 
breakage.  Heat  strongly  at  the  last.  The  calculation  may  be 
left  to  the  student.  Compare  your  result  with  that  calculated 
from  the  formula  according  to  the  method  of  the  textbook, 
pages  89  and  385. 

Place  the  copper  in  the  receptacle  provided. 

EXERCISE  79 

THE   ATOMIC   WEIGHT  OF   COPPER  BY  OXIDIZING 
REDUCED  COPPER 

(Quantitative) 

Apparatus.  —  Porcelain  crucible  without  cover.  Triangle.  Glass 
rod.  Balance. 

Materials.  —  Reduced  copper  from  Exercises  77  and  78. 

Method.  —  Although  ordinary  copper  cannot  be  completely  changed 
to  oxide  by  heating,  the  reduced  copper  from  Exercises  77  and  78 
passes  readily  into  cupric  oxide  at  a  red  heat  in  the  air. 

Weigh  the  crucible  and  weigh  in  it  from  0.5  gram  to  1  gram 
of  copper,  which  must  previously  be  finely  powdered  in  a  mortar. 
Heat  to  redness  for  ten  minutes.  Let  cool  slightly  and  turn 
over  with  a  glass  rod.  Heat  again  to  redness  for  ten  minutes ; 
cool  and  weigh.  The  calculation  is  similar  to  that  of  the  atomic 
weight  of  copper  by  reducing  cupric  oxide  (Exercise  77). 


THE  ATOMIC  WEIGHT  OF  SULPHUR  113 

EXERCISE  80 
THE  ATOMIC   WEIGHT   OF   SULPHUR 

(Quantitative) 

Apparatus.  —  Porcelain  crucible  and  cover.  Triangle.  Balance. 
Glass  rod. 

Materials.  —  Cadmium  oxide.     Flowers  of  sulphur. 

Method.  —  Cadmium  oxide  when  heated  with  sulphur  passes  into 
cadmium  sulphide :  — 

CdO  +  3S->CdS+  SO2. 

From  the  increase  in  weight  of  the  crucible,  the  atomic  weight  of 
sulphur  can  be  calculated. 

Weigh  accurately  a  crucible  without  cover  and  weigh  in  it 
exactly  1  gram  of  cadmium  oxide.  Add  a  gram  of  sulphur 
roughly  weighed.  Since  the  excess  of  sulphur  will  be  driven 
off  by  heat,  the  exact  weighing  of  the  sulphur  would  be  useless. 
Mix  well  with  a  glass  rod  and  dust  off  the  rod  into  the  crucible. 
Cover  the  crucible  and  place  it  on  the  triangle. 

Turn  the  burner  flame  to  full  height  and  take  the  burner  in 
the  hand.  Heat  carefully,  keeping  the  flame  in  motion  and 
making  sure  that  all  parts  of  the  crucible  are  heated,  but  not 
to  redness.  Especially  avoid  letting  the  bottom  glow.  See  that 
the  upper  part,  where  the  crucible  and  lid  join,  is  thoroughly 
heated.  Blue  flames  of  burning  sulphur  appear  here  between 
lid  and  crucible.  When  they  vanish,  the  heating  is  sufficient. 
Do  not  heat  too  long. 

Calculation.  —  We  start  with  the  proportion  :  — 

weight  CdO  :  weight  CdS  : :  mol.  weight  CdO  :  mol.  weight  CdS, 

mol.  weight  CdS  =  weight  CdS  x  mol.  weight  CdO 

weight  CdO 

Since  the  aotmic  weight  of  cadmium  is  112.5  and  that  of  oxygen 
16  we  have  :  — 


114       LABORATORY    STUDIES   IN   CHEMISTRY 

atomic  Height  S  +  112.5  =  weight  CdS  x  128.5 

weight  CdO 

atomic  weight  S  =  weight  CdS  x  128.5 
weight  CdO 


EXERCISE  81 
THE  FORMULA   OF   ZINC   CHLORIDE 

(Quantitative) 

Apparatus.  —  Conical  flask  (capacity  80  c.c.).  Asbestos  plate  (wire 
gauze  can  be  used  with  care) .  Small  watch  glass.  Balance. 

Material.  —  Sheet  zinc. 

Method.  —  Zinc  dissolves  in  hydrochloric  acid  to  form  zinc  chloride, 
which  can  be  obtained  in  anhydrous  condition  by  evaporation. 

Results  are  good  only  if  the  directions  are  exactly  followed. 

Weigh  the  flask,  which  must  be  dry,  and  place  in  it  about  2 
grams  of  zinc,  accurately  weighed.  Add  10  c.c.  concentrated 
hydrochloric  acid,  cover  with  a  watch  glass  and  heat  gently 
witii  a  small  flame  (which  does  not  touch  the  asbestos  plate) 
until  the  zinc  is  dissolved.  Then  increase  the  flame  and 
boil  the  liquid  until  the  water  is  evaporated.  This  is  indi- 
cated by  the  fact  that  the  formation  of  bubbles  practically 
stops. 

Now  reduce  the  flame  until  it  does  not  quite  touch  the  asbestos 
plate  and  remove  the  watch  glass.  The  zinc  chloride  will 
solidify  and  then  melt.  Just  as  soon  as  it  melts,  stop  heating 
and  weigh  when  cold  enough  to  handle.  Zinc  chloride  absorbs 
water  from  the  air,  and  if  the  flask  is  allowed  to  stand  long 
before  weighing,  it  should  be  corked. 

Calculation.  — 

You  have  the  weight  of  the  zinc :  the  weight  of  the  zinc 
chloride  is  obtained  by  subtracting  the  weight  of  the  flask 
from  the  final  weight.  The  chlorine  is,  of  course,  the  differ- 
ence between  the  zinc  and  the  zinc  chloride. 


OXYGEN   IN  POTASSIUM  CHLORATE  115 

Divide  the  weight  of  the  zinc  by  the  atomic  weight  of  zinc, 
and  that  of  the  chlorine  by  the  atomic  weight  of  chlorine. 
You  will  obtain  decimal  fractions  which  will,  however,  be  seen 
to  bear  to  each  other  approximately  the  relation  of  small 
whole  numbers.  These  are  the  numbers  which  must  be  added 
to  the  symbols  to  give  the  formula.  An  example  of  the  calcu- 
lation is  given  in  the  textbook,  page  385. 


EXERCISE  82 

PERCENTAGE  OF  OXYGEN  IN  POTASSIUM 
CHLORATE 

(Quantitative) 

Apparatus.  —  Pipestem  triangle.  Porclain  crucible  with  cover. 
Balance.  Small  test  tubes. 

Materials.  —  Potassium  chlorate.  Potassium  chloride.  Silver 
nitrate  solution.  Distilled  water. 

Method.  —  The  oxygen  is  driven  off  by  heat  and  the  loss  in 
weight  obtained. 

KC103->KC1  +  30. 

Dissolve  0.2  c.c.  potassium  chlorate  in  5  c.c.  distilled  water. 
In  another  tube,  dissolve  0.2  c.c.  potassium  chloride  in  5  c.c. 
distilled  water.  Add  ten  drops  silver  nitrate  solution  to  each 
tube.  Results  ?  Potassium  chlorate  is  apt  to  contain  a  trace 
of  potassium  chloride,  so  that  a  slight  precipitate  may  be  ob- 
tained in  the  first  tube  also.  Weigh  crucible,  with  cover,  place 
the  cover  on  the  balance  pan  beside  the  "crucible,  and  weigh  in 
the  crucible  1  gram  of  potassium  chlorate.  Heat  carefully  for 
ten  minutes,  keeping  flame  in  motion ;  apply  the  full  heat  of 
the  burner  for  five  minutes  more,  cool  and  weigh  without  re- 
moving cover.  Calculate  the  percentage  of  oxygen,  and  com- 
pare it  with  that  calculated  from  the  formula. 

Examine  the  residue  in  the  crucible.  What  is  it  ?  Dissolve 
it  in  water  and  add  silver  nitrate  solution.  Result  ? 


116        LABORATORY   STUDIES   IN   CHEMISTRY 

^  EXERCISE  83 

THE  EFFECT   OF  HEAT  AND   OF  ACIDS   ON 
CARBONATES 

Apparatus.  —  Wire  gauze.  Hard  glass  test  tube  with  one-hole 
rubber  stopper  aud  delivery  tube  bent  at  right  angle.  Evaporating 
dish.  Glass  rod.  Small  test  tubes. 

Materials.  —  Calcite  (crystals  or  cleavage  pieces).  Magnesite. 
Malachite  (powder).  Commercial  copper  carbonate  can  be  used  in- 
stead of  malachite.  White  lead.  Lime.  Red  litmus  paper.  Lime- 
water. 

Method.  —  Most  carbonates  are  decomposed  by  heat,  giving  off  car- 
bon dioxide  and  leaving  a  residue  of  the  oxide  of  the  metal.  Carbon 
dioxide  escapes  when  carbonates  are  dissolved  in  acids. 

(a)  Select  two  small  pieces  of  calcite,  not  more  than  1  cm. 
(0.4  in.)  long.  Keep  one  for  comparison.  Support  the  other  on 
wire  gauze  and  heat  it  with  the  full  power  of  the  burner  for  ten 
minutes  or  more.  Compare  with  the  unheated  piece.  Look 
especially  at  the  edges  for  a  change.  If  no  distinct  alteration 
has  occurred,  continue  heating  until  there  is  a  visible  result. 
Write  the  equation  for  the  chemical  change  which  has  taken 
place. 

Your  equation,  if  correct,  will  call  for  the  production  of  two 
substances,  one  of  which  is  lime.  Verify  this  as  follows : 
Place  a  piece  of  red  litmus  paper  in  a  clean  dish  and  upon  it 
a  fragment  of  good  lime  2  mm.  (0.08  in.)  in  diameter.  Moisten 
the  lime  with  two  drops  of  water,  using  a  glass  rod.  Is  there 
any  evidence  of  chemical  change  ?  Write  the  equation.  Now 
add  enough  water  to  moisten  both  lime  and  paper  and  wait 
several  minutes.  What  does  the  change  in  the  paper  indicate  ? 

Clean  the  dish,  place  your  unheated  crystal  on  a  fresh  piece 
of  red  litmus  paper,  and  treat  it  in  the  same  way.  Is  there 
any  change? 

Now  treat  the  crystal  which  has  been  heated  in  exactly  the 
same  manner.  Is  your  suspicion  that  lime  is  produced  verified  ? 

The  second  substance  called  for  by  your  equation  for  the 


EFFECT  OF  HEAT  AND  ACIDS  ON  CARBONATES     117 

heating  of  calcite  is  a  gas.  The  difficulty  about  verifying  its 
formation  is  that  the  temperature  at  which  calcite  decomposes 
is  so  high  that  a  glass  tube  would  be  melted. 

(6)  Magnesite  differs  from  calcite  in  containing  magnesium 
instead  of  calcium.  It  behaves  in  the  same  way  when  heated 
except  that  the  temperature  required  is  not  nearly  so  high. 
Select  two  pieces  of  it  about  1  cm.  in  diameter.  Reserve  one  for 
comparison.  Heat  the  other  in  the  hard  glass  test  tube.  The 
delivery  tube  dips  into  some  clear  limewater  in  a  test  tube. 
The  heat  should  be  gentle  at  first  and  the  final  temperature 
need  not  be  high  enough  to  soften  the  glass.  Watch  the 
limewater  intently  during  the  whole  progress  of  the  experi- 
ment. Take  out  the  stopper  before  letting  the  hard  glass  tube 
cool. 

What  gas  escaped?  Compare  the  magnesite  which  has 
been  heated  with  the  unheated  mineral  as  regards  appearance 
and  cohesion.  Compare  the  two  in  their  behavior  when 
placed  on  red  litmus  paper  and  moistened.  Wait  patiently 
for  a  result,  as  the  action  may  be  slow. 

(c)  Malachite  is  more  complex  because  it  is  a  basic  carbon- 
ate.    This  means  that  it  contains  copper  hydroxide  as  well  as 
copper  carbonate.     Heat  1  c.c.  of  the  powder  in  the  same  tube 
used  for  the  magnesite,  first  wiping  the  tube  out  thoroughly 
with  paper.     The  tube  must  be  horizontal  and  the  heat  very 
gentle.     The  delivery  tube  dips  into  a  fresh  portion  of  lime- 
water.     There  are  three  products.     What  are  they  and  what 
is  the  evidence  for  their  formation  ? 

The  red  litmus  test  would  be  useless  in  this  case. 

(d)  Heat  1  c.c.  of  white  lead  in  the  same  way  as  malachite. 
Like  malachite,  white  lead  is  a  basic  carbonate.     Its  formula 
is  Pb(OH),  2  PbC03.     What  three  products  are  formed  ? 

(e)  Place  a  2  mm.  (0.08  in.)  bit  of  calcite  in  a  test  tube,  add 
2  c.c.  of  water  and  2  c.c.  of  concentrated  hydrochloric  acid. 
Result  ?    What  gas  escapes  ?     Complete  the  equation :  — 

CaCOq  +  x  HC1  ->  CaCL  +  H9O  +.... 


118       LABORATORY   STUDIES   IN   CHEMISTRY 

Repeat,  using  nitric  acid  instead  of  hydrochloric.  Complete 
the  equation :  — 

CaC03  +  x  HN03  ->  Ca(NO3)2  +  H2O  4-  -.. 

In  the  same  way,  investigate  the  interaction  of  magnesite 
and  of  malachite  with  hydrochloric  and  also  with  nitric  acid. 
Use  a  gentle  heat,  if  necessary.  Complete  the  equations  :  — 

MgC03  +  x  HC1  ->  MgCl2+  H20  +  .», 
MgC03  +  x  HN08  ->  Mg(N03)2  +  HaO  +  .... 

In  the  case  of  malachite,  the  equations  are  more  difficult  and 
are,  therefore,  given  in  full :  — 

CuCO3Cu(OH)2  +  4  HC1  ->  2  CuCl2  +  3  H2O  +  CO2, 

(Malachite) 

CuCO3Cu(OH)2  +  4  HNO3  ->  2  Cu(NO3)2  +  3  H2O  +  CO2. 

Make  a  general  statement  about  the  action  of  acids  on  car- 
bonates. How  could  you  ascertain  whether  a  substance  sub- 
mitted to  you  was  a  carbonate  or  not  ? 

EXERCISE  84 

THE   EFFECT   OF   HEAT   OK  A   CARBONATE  ' 

(Quantitative) 

Apparatus.  —  Porcelain  crucible.  Pipestem  triangle.  Small  test 
tubes.  Balance. 

Materials.  —  Magnesium  carbonate  (powdered  magnesite). 
Method.  — See  Exercise  83. 

(a)  Heat,  in  a  test  tube,  a  mixture  of  2  c.c.  hydrochloric 
acid  and  5  c.c.  water  nearly  to   boiling.     Remove   from   the 
flame   and   add  1  c.c.  powdered  magnesite.     Result?-    What 
gas  escapes  ? 

(b)  Weigh  a  crucible  without  the  cover  and  weigh  in  it  a 
gram  of  fine  magnesite  powder.     Heat  gently  at  first,  finally 
apply  the  full  heat  of  the  flame  for  fifteen  minutes,  cool  and 
weigh.    If  time  permits,  the  exactness  of  the  result  is  increased 


BORIC  ACID  AND  BORAX  119 

by  reheating  sharply  for  five  minutes  and  weighing  again  to 
see  if  the  decomposition  is  complete.  Use  the  lowest  weight 
obtained  in  your  calculation. 

The  loss  in  weight  is  carbon  dioxide  :  — 

MgCO3  ->  MgO  +  CO2. 

What  is  the  percentage  of  carbon  dioxide  yielded  by  mag- 
nesite  according  to  your  results  ?  How  does  your  result  agree 
with  that  calculated  from  the  equation  ? 

(c)  Test  the  substance  in  the  crucible  by  throwing  it  into 
a  warm  mixture  of  hydrochloric  acid  and  water  as  in  (a). 
Result? 

EXERCISE  86 l 
BORIC  ACID  AND  BORAX 

Apparatus.  —  Trip  scales.  Graduated  cylinder.  Beaker.  Dish. 
Small  dry  test  tube.  Glass  rod. 

Materials.  —  Boracite.  Boric  acid.  Borax.  Sodium  carbonate. 
Alcohol. 

Method.  —  Boric  acid  is  produced  when  borates  are  treated  with 
active  acids.  Borax  is  obtained  when  boric  acid  or  a  borate  is  treated 
with  a  solution  of  sodium  carbonate. 

(a)  Mix  10  grams   powdered  boracite  with  10  c.c.  concen- 
trated hydrochloric  acid  and  10  c.c.  water  in  a  dish.     Heat 
gently  for  ten  minutes.     Filter  hot  and  let  cool.     The  crystals 
are  boric  acid,  H3B03.     Boracite  is  chiefly  magnesium  borate. 
What,  then,  is  the  action  of  hydrochloric  acid  upon  it  ?    What 
magnesium  compound  must  be  contained  in  the  liquid  which 
covers  the  crystals  ? 

(b)  Dissolve  12  grams  boric  acid  in  60  c.c.  of  boiling  water 
in  a  dish.     Slowly  add  10  grams  anhydrous  sodium  carbonate. 
Recalling  the  behavior  of   carbonates   with   acids,  what    gas 
escapes  ?     What  must  exist  in  the  liquid  ?     Evaporate  until 

1  If  the  period  is  short,  it  may  be  convenient  to  distribute  (a),  (6) 
and  (c)  to  different  students. 


120        LABORATORY   STUDIES   IN   CHEMISTRY 

the  liquid  is  half  gone  and  let  cool.  Borax  separates.  Com- 
pare the  crystals  with  those  of  boric  acid.  Complete  the 
equation :  — 

Na2C03  +  x  H3B03  ->  Na2B4O7  +  y  H2O  +  .... 

(Boric  acid)          (Borax) 

(c)  Slowly  add  10  c.c.  concentrated  sulphuric  acid  to  15  c.c. 
water.  Pour  this  liquid  into  a  hot  solution  of  10  grams  borax 
in  50  c.c.  water  in  a  beaker.  Let  cool.  Result  ?  Complete 
the  equation :  — 

Na2B4O7  +  H2SO4  +  x  H2O  ->  y  H3BO3  +  Na2SO4. 

(cT)  If  time  permits,  test  borax  for  water  of  crystallization 
by  gently  heating  2  c.c.  from  the  stock  bottle  in  a  dry,  clean 
test  tube  clamped  in  a  horizontal  position. 

(e)  In  a  clean  dish  mix  1  c.c.  of  borax  with  0.5  c.c.  of  con- 
centrated sulphuric  acid.  Add  2  c.c.  alcohol  and  set  fire  to 
the  liquid.  Result  ?  This  is  a  test  for  boric  acid  or  a  borate. 

EXERCISE  86 

THE   ATOMIC   WEIGHT   OF  MAGNESIUM 

Apparatus.  —  Wide-mouthed  bottle  holding  about  400  c.c.     Gradu- 
ated 100  c.c.  cylinder.     Glass  plate.     Balance.     Agate  pan. 
Material.  —  Magnesium  ribbon. 

Method.  —  Magnesium  dissolves  in  hydrochloric  acid  :  — 
Mg  +  2  HCl-^MgCl2  4-  H2. 

The  atomic  weight  of  magnesium  can  be  calculated  from  the  volume 
of  the  hydrogen  liberated. 

Weigh  accurately  not  more  than  0.4  gram  of  magnesium 
ribbon.  The  weight  should  be  accurate  to  a  milligram.  If 
your  balance  is  not  exact  enough  for  this,  weigh  2  m.  of  the 
ribbon  and  calculate  by  proportion  the  length  you  must  cut 
off  in  order  to  get  the  weight  you  desire  to  take.  If  your 
bottle  holds  less  than  400  c.c.,  reduce  the  weight  of  magnesium 
proportionally,  taking  not  more  than  0.1  gram  for  each  100  c.c. 


THE  ATOMIC  WEIGHT   OF  MAGNESIUM         121 

capacity.  Coil  the  ribbon  into  a  spiral,  smaller  than  the  mouth 
of  the  bottle. 

Place  40  c.c.  of  concentrated  hydrochloric  acid  in  the  bottle. 
Fill  the  bottle  with  water,  adding  the  water  carefully  so  as  to 
allow  the  acid  to  remain  at  the  bottom.  With  the  aid  of  a 
glass  plate  invert  the  bottle  in  an  agate  pan  of  water.  The 
water  should  be  about  5  cm.  deep  in  the  pan.  The  bottle  must 
not  contain  air  bubbles.  If  a.  little  air  enters,  withdraw  the 
bottle  carefully,  using  the  glass  plate,  set  it  upright  upon  the 
desk,  add  water  until  it  is  completely  filled,  and  try  again. 

Put  the  coil  of  magnesium  ribbon  in  the  pan,  slide  the 
mouth  of  the  bottle  (under  water)  over  it  and  set  it  down. 

What  gas  collects  ?  What  other  substance  must  be  formed 
and  dissolve  in  the  water  ? 

When  the  action  is  over,  add  water  to  the  pan  or  remove 
water,  as  may  be  necessary  to  make  the  level  of  the  water 
inside  and  outside  the  same.  Why  ?  Tightly  cover  the  bottle 
with  the  glass  plate  and  remove  it  from  the  water,  without 
allowing  any  water  to  escape  from  the  bottle. 

Set  the  bottle  upright  on  the  desk,  strike  a  match,  take  off 
the  glass  plate,  and  instantly  hold  the  burning  match  in  the 
mouth  of  the  bottle.  Result  ? 

With  the  graduated  cylinder,  measure  (1)  the  water  left  in 
the  bottle,  (2)  the  total  capacity  of  the  bottle.  Subtract  (1) 
from  (2)  to  obtain  the  volume  of  the  hydrogen. 

Calculation.  —  Subtract  one  fourteenth  from  this  volume  for 
expansion,  due  to  the  fact  that  the  hydrogen  is  not  measured  at 
standard  temperature.  Multiply  the  remainder  by  one  fiftieth 
and  subtract  to  correct  for  the  water  vapor,  which  is  measured 
with  the  hydrogen,  since  it  is  collected  over  water.  The  re- 
mainder will  be  approximately  the  volume  which  your  hydro- 
gen would  occupy  4at  STP.1  Since  the  weight  of  1  c.c.  of 
hydrogen  at  STP  is  0.00009  gram,  the  volume  of  your  hydro- 
gen in  cubic  centimeters  multiplied  by  0.00009  gives  its  weight 
in  grams. 

1  STP  means  standard  temperature  and  pressure,  0°  and  760  mm. 


122       LABORATORY   STUDIES   IN    CHEMISTRY 

The  equation :  — 

Mg  +  2  HC1  ->  MgCl2  +  H2 

shows  that  the  atomic  weight  of  magnesium  in  grams  would 
set  free  two  atomic  weights  or  2.02  grams  of  hydrogen.  Hence, 
use  the  proportion :  — 

Weight  in  grams  of  your  hydrogen  :  2.02  : :  weight  in  grams  of  magne- 
sium taken  :  atomic  weight  of  magnesium. 

Sample  Calculation.1 — A  student  found  that  0.4  gram  of 
magnesium  produced  400  c.c.  of  hydrogen,  measured  under  the 
conditions  of  the  experiment.  Since -our  measurements  are 
made  with  a  cylinder  which  does  not  read  to  fractions  of  a 
cubic  centimeter,  it  is  a  waste  of  time  to  retain  fractions  of  a 
cubic  centimeter  in  the  calculation. 

400  c.c.  x  YJ  =  29  c.c.  (correction  for  expansion). 
400  c.c.  -  29  =  371  c.c. 

371  c.c.  x  sV  =  7  c-c-   (correction  for  water  vapor) . 
371  c.c.  -  7  c.c.  =  364  c.c.  (volume  at  STP). 
364  c.c.  x  0.00009  =  0.03276  gram  (weight  of  hydrogen). 
0.03276:2.02  ::  0.4.x. 
x  =  24.66. 

1  This  calculation  is  approximate,  but  the  error  does  not  exceed  the 
probable  error  of  the  experimental  measurement.  The  teacher  may, 
however,  prefer  to  calculate  the  result  by  the  more  exact  methods  ex- 
plained in  Chapter  30  of  the  textbook.  A  third  method  is  for  the  teacher 
to  calculate  the  weight  of  1  c.c.  of  moist  hydrogen,  under  the  experimen- 
tal conditions.  This  does  not  vary  widely  from  0.000082  gram.  The 
student  then  calculates  the  weight  of  the  hydrogen  by  multiplication  and 
applies  the  proportion  given  above. 


THE   PRODUCTION  OF  A  DOUBLE  SALT         123 

EXERCISE  87 
THE  PRODUCTION   OF  A  DOUBLE   SALT 

Apparatus.  —  Two  large  test  tubes.  Three  small  test  tubes. 
Beaker.  Glass  rod.  Trip  scales.  Graduated  cylinder.  Lens. 
Funnel. 

Materials.  —  Copper  sulphate  (commercial).  Ammonium  sulphate 
(commercial).  Barium  chloride  solution.  Lime.  Filters.  Iron 
nails. 

Method.  —  When  concentrated  hot  solutions  of  copper  sulphate  and 
of  ammonium  sulphate  are  mixed  and  allowed  to  cool,  copper  ammo- 
nium sulphate  (CuSO4,  (NH4)2SO4,  6  H2O)  is  deposited  in  light  blue 
crystals. 

Using  decigrams1  as  your  unit,  weigh  off  the  molecular  weight 
of  copper  sulphate  (CuS045H20).  Hold  a  large  test  tube 
nearly  horizontal  and  place  the  copper  sulphate  in  it.  Add 
30  c.c.  water,  clamp  the  tube  at  an  angle  of  45°,  and  place  under 
it  a  small  flame,  just  sufficient  to  heat  the  liquid  to  boiling. 

Weigh  off  the  molecular  weight  of  ammonium  sulphate 
(NH4)2S04  in  decigrams,  and  treat  it  in  the  same  way,  using 
only  20  c.c.  of  water. 

When  both  salts  are  completely  dissolved,  mix  the  solutions 
in  a  clean  beaker  and  let  cool.  The  double  salt  deposits.  If 
no  deposit  forms,  the  solution  is  supersaturated,  and  it  may  be 
left  as  an  exercise  for  the  student  to  devise  a  method  of  caus- 
ing crystallization  to  occur.  Scrape  the  crystals  on  a  filter, 
using  a  glass  rod.  Examine  the  double  salt  with  a  lens  and 
compare  it  with  copper  sulphate  and  with  ammonium  sulphate. 
Dissolve  2  c.c.  of  the  double  salt  in  15  c.c.  hot  water  and  divide 
the  liquid  into  three  portions  in  small  test  tubes.  To  one  por- 
tion add  a  few  drops  of  barium  chloride  solution.  Result  ? 
Is  the  double  salt  a  sulphate  ?  To  the  second  portion  add  an 

1  Although  both  sulphates  are  cheap,  the  teacher  may  prefer  to  use 
centigrams  as  a  unit  and  one  tenth  the  volume  of  water.  Small  test  tubes 
should  then  be  used. 


124         LABORATORY  STUDIES  IN  CHEMISTRY 

iron  nail  arid  let  stand.  Result?  To  the  third  portion  add 
2  c.c.  of  lime  and  heat  gently.  Note  odor  of  the  gas  which 
escapes.  Test  it  with  red  litmus  paper.  Then  hold  in  it  a  rod 
wet  with  hydrochloric  acid.  Result  ?  What  is  proved  by 
these  three  tests  ? 


APPARATUS   AND   SPECIAL  MATERIALS 

The  following  list  includes  the   apparatus   and  chemicals 
needed  for  the  experiments  in  the  Laboratory  Studies. 

Agate  pan,  round,  30  x  7.5  cm.  (12  x  3  in.). 

Asbestos  boards,  10  cm.  square. 

Asbestos  paper.  • 

Balance  —  beam  balance  sensitive  to  a  milligram,  if  possible,  with 
weights  from  50  g.  to  1  mg.  Such  an  instrument  will  cost  about 
ten  dollars,  slightly  more  if  purchased  with  case  provided  with 
sliding  door  and  glass  sides  and  back.  Duty-free  importation  is 
assumed. 

Balance  —  trip  scales  sensitive  to  a  decigram  with  weights  from  100 
g.  to  10  g. 

Barometer. 

Beakers,  about  100  c.c.  capacity. 

Blowpipe,  simplest  form. 

Bottles,  common  salt-mouth,  about  400  c.c.  capacity,  no  stopper. 

Bottles,  gas  generating,  300  c.c. 

Bunsen  burner  with  wing-top. 

Burette,  Mohr  form  with  rubber  tube  and  pinchcock,  50  c.c.,  gradu- 
ated to  T^  c.c.  The  Geissler  burette  with  glass  stopcock  does  not 
work  well  in  the  hands  of  a  beginner. 

Cigar  lighters  (tobacconists'  splints)  for  spark  test. 

Clamps  (burette),  one  for  each  stand. 

Cobalt  glass,  10  cm.  square. 

Corks  to  fit  large  and  small  test  tubes. 

Crucibles,  porcelain,  with  cover,  capacity  25  c.c. 

Deflagrating  spoon,  iron,  small. 

Dennison  labels,  Nos.  201,  213,  223. 

Dishes,  iron,  capacity  70  to  100  c.c. 

Dishes,  lead,  capacity  50  to  100  c.c. 

Dishes,  porcelain  evaporating,  capacity  125  c.c. 

File,  small  triangular. 

Filter  paper. 

125 


126        LABORATORY   STUDIES   IN   CHEMISTRY 

Filters,  cut  ordinary,  10  cm. 

Flask,  volumetric,  1  liter. 

Flask,  volumetric,  6  liters  (optional,  but  very  convenient). 

Flasks,  Erlenmeyer,  80  c.c. 

Flasks,  ordinary,  300  c.c. 

Forceps,  small  steel,  cheapest  form. 

Funnels,  75  mm.  diameter. 

Funnels,   dropping,  80  c.c.  capacity  (optional,  but   convenient).     A 

fair  substitute  can  be  made  by  cutting  a  thistle  tube  and  uniting 

by  a  rubber  tube  bearing  a  clamp. 
Glass  plates  8  cm.  square  for  covering  bottles. 
Glass  rod,  3  mm.  diameter.  * 

Glass  tubing,  7  mm.  outside  diameter. 
Glass  tubing,  14  mm.  outside  diameter,  hard  glass. 
Graduated  cylinder,  100  c.c.  graduated  to  1  c.c. 
Hammer  with  heavy  iron  plate  for  crushing  minerals. 
Kipp  generator,  simplest  form  (optional). 
Lens,  Coddiugton,  3  cm.  focus. 
Magnet,  small  horseshoe. 
Medicine  dropper. 
Meter  stick,  centimeters  and  millimeters  on  one  side,  inches  and 

fractions  on  other. 
Miner's  safety  lamp. 
Mohr  pinchcocks. 

Mortar,  6  cm.  porcelain,  with  pestle. 
Platinum  foil,  25  mm.  square. 
Platinum  wire,  B.  &  S.  gauge,  No.  25. 
Pliers,  gas,  small. 

Retort,  150  c.c.  capacity,  glass  stopper. 
Rubber  bands  (small). 
Rubber  stoppers,  No.  0  (1-hole)  ;  No.  2  (1-hole)  ;  No.  3  (solid,  1-hole, 

2-hole)  ;  No.  5  (1-hole,  2-hole). 

Rubber  tubing  for  gas  connections,  cloth  impression,  8  mm.  bore. 
Rubber  tubing  for  apparatus  connections,  heavy  wall,  4  mm.  bore.  (The 

best  grade  of  rubber  stoppers  and  tubing  should  be  purchased.) 
Rubber  tubing  to  renew  clamps,  cloth  impression,  15  mm.  bore. 
Scissors,  ordinary,  for  cutting  paper,  rubber  tubing,  etc. 
Shears,  tinner's,  for  cutting  sheet  metals. 

Stand,  about  150  cm.  high,  with  one  ring  7  cm.  or  8  cm.  in  diameter. 
Test  tubes,  200  x  25  mm, 


APPARATUS  AND   SPECIAL  MATERIALS 


127 


Test  tubes,  150  x  18  mm. 

Test  tubes,  100  x  12  mm.  (hard  glass). 

Thermometer,  reading  from  - 10°  C.  to  150°  C. 

Thistle  tubes  (small). 

Waste  jar,  4  gallon,  earthenware  glazed. 

Watch  glasses,  5  cm.  and  8.5  cm. 

Wire  cutter  (electrician's,  small). 

Wire  gauze,  iron,  10  cm.  square. 


CHEMICALS,   ETC. 


Acid,  Acetic. 
Acid,  Boric. 
Acid,  Formic. 
Acid,  Hydrochloric. 
Acid,  Nitric. 
Acid,  Oxalic. 
Acid,  Sulphuric. 
Alcohol,  95  per  cent  grain. 
Alcohol,  Wood  Spirit. 
Aluminium  (sheet  or  turnings). 
Aluminium  Sulphate. 
Ammonia  Water. 
Ammonium  Carbonate. 
Ammonium    Chloride    (commer- 
cial). 

Ammonium  Bichromate. 
Ammonium  Molybdate  (solution). 
Ammonium  Nitrate. 
Ammonium  Sulphate. 
Ammonium  Sulphocyanide. 
Aniline  Red. 
Arsenic,  Metallic. 
Arsenious  Oxide. 
Asbestos  Fiber. 
Barium  Chloride. 
Barium  Nitrate. 
Boneblack. 
Borax. 
Bromine. 


Cadmium  Oxide. 

Calcium  (metallic). 

Calcium  Carbide. 

Calcium       Carbonate       (marble 

cracked  in  1  cm.  fragments). 
Calcium  Carbonate  (precipitated 

chalk). 
Calcium    Chloride    (commercial 

dry). 

Calcium  Fluoride  (powder). 
Calcium  Nitrate. 
Calcium  Oxide  (lime). 
Calcium  Sulphate  (powder). 
Candles  (Christmas-tree  candles). 
Carbon  (charcoal  ordinary). 
Carbon  (charcoal,  prismatic   for 

blowpipe  use). 
Carbon  (charcoal  powder). 
Carbon  Bisulphide. 
Cardboard. 
Chloroform. 
Chrome  Alum. 
Coal  (bituminous). 
Cobalt  Chloride. 
Cobalt  Nitrate. 
Cobalt  Sulphate. 
Cochineal. 
Congo  Red. 
Copper  Sheet  (ordinary). 


128        LABORATORY  STUDIES  IN  CHEMISTRY 


Copper  Sheet,  0.05  mm.  thick. 
Cotton  Cloth  (colored). 
Cotton  Cloth  (muslin,  white). 
Cupric  Carbonate  (basic).     . 
Cupric  Chloride. 
Cupric  Oxide. 

Cupric  Sulphate  (commercial). 
Cupric  Sulphate  (C.  P.) 
Cuprous  Oxide. 
Emery  paper  (fine). 
Ether. 

Ferrous  Ammonium  Sulphate. 
Ferrous  Sulphate. 
Flannel  (white). 
Glucose. 
Glue  (solid). 
Gold  Leaf. 
Hydrogen  Peroxide. 
Iodine. 

Iron  (powder  by  alcohol). 
Iron  Alum  (ferric  ammonium  sul- 
phate). 

Iron  Chloride  (ferric). 
Iron  Filings. 
Iron  Nails. 

Iron  Sulphide  (ferrous). 
Kerosene. 

Lead  (granulated,  test  lead). 
Lead  Foil  (tea  lead). 
Lead  Nitrate. 
Lead  Oxide  (litharge). 
Lead,  Red. 
Lead,  White. 
Lithium  Chloride. 
Litmus  Cubes. 

Litmus  Paper  (red  and  blue). 
Magnesium  Oxide. 
Magnesium  Ribbon. 
Magnesium  Sulphate. 
Malachite  Green. 


Manganese  Dioxide  (powder). 

Mercuric  Chloride. 

Mercuric  Oxide. 

Mercurous  Nitrate. 

Mercury. 

Molasses. 

Nickel  Nitrate. 

Paraffin. 

Paste  (photographic,  in  tube). 

Phenol -phthalein . 

Phosphorus  (red). 

Picture  Cord. 

Pins. 

Potassium  Alum. 

Potassium  Bromide. 

Potassium  Carbonate  (commer 
cial). 

Potassium  Chlorate. 

Potassium  Chloride. 

Potassium  Chromate. 

Potassium  Cyanide. 

Potassium  Dichromate. 

Potassium  Hydroxide. 

Potassium  Iodide. 

Potassium  Nitrate. 

Potassium  Permanganate. 

Potassium  Sulphate. 

Pyrogallol. 

Rosin. 

Sand. 

Sandpaper. 

Silver  Nitrate. 

Soda  Lime. 

Sodium. 

Sodium  Acetate  (fused). 

Sodium  Ammonium  Phosphate. 

Sodium  Carbonate  (dry). 

Sodium  Carbonate  Crystals  (com- 
mercial). 

Sodium  Chloride  (C.  P.), 


APPARATUS  AND  SPECIAL  MATERIALS 


129 


Sodium  Chloride  (common  salt). 

Sodium  Hydrogen  Carbonate. 

Sodium  Hydrogen  Phosphate. 

Sodium  Hydrogen  Sulphate. 

Sodium  Hydroxide. 

Sodium  Nitrate. 

Sodium  Nitrite. 

Sodium  Potassium  Tartrate  (Ro- 
chelle  salt). 

Sodium  Sulphate. 

Sodium  Thiosulphate  (commer- 
cial). 

Stannic  Oxide. 

Stannous  Chloride. 

Starch. 

Strontium  Chloride  (optional). 

Strontium  Nitrate. 

Sugar  (ordinary). 

Sulphur,  Flowers. 

Sulphur,  Roll. 

Superphosphate  (fertilizer). 

Tannic  Acid. 


Tartar  Emetic. 

Tin  Chloride. 

Tin  Foil  (pure,  free  from  lead). 

Thread. 

Toluol. 

Vaseline. 

Water,  Distilled. 

Wire,    Copper    (No.   12  B.  &  S. 

gauge). 
Wire,  Copper  (No.  20  B.  &   S. 

gauge). 
Wire,   Copper   (No.   30  B.  &  S. 

gauge). 
Wire,  German  Silver  (No.  36,  Be 

&  S.  gauge). 
Wire,  Iron,  No.  20. 
Zinc  Dust. 
Zinc,  Mossy. 
Zinc  Oxide. 
Zinc  (sheet). 
Zinc  Sulphate. 


MINERALS 


Boracite. 

Calcite  (cleavage  pieces). 

Chalcopyrite. 

Chrysocolla. 

Cinnabar  (10  per  cent). 

Galenite. 

Gypsum. 


Magnesite. 

Orthoclase. 

Phosphate  Rock. 

Pyrite. 

Rhodonite. 

Siderite. 

Sphalerite. 


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